Alveolar Rhabdomyosarcoma

MONDO:0009994 Pathograph 26 Show in embeddings browser rhabdomyosarcoma

Alveolar rhabdomyosarcoma (ARMS) is an aggressive pediatric soft tissue sarcoma characterized by skeletal muscle differentiation and distinctive chromosomal translocations involving PAX3 or PAX7 fused to FOXO1. Among fusion-positive tumors, PAX3-FOXO1 arising from t(2;13)(q35;q14) is the dominant fusion subtype, reported in roughly 70-90% of cases, and confers a worse prognosis. PAX7-FOXO1 from t(1;13)(p36;q14) accounts for most of the remaining fusion-positive cases and is generally associated with somewhat better outcomes. Approximately 20% are fusion-negative and behave more like embryonal rhabdomyosarcoma. The PAX-FOXO1 fusion proteins function as aberrant transcription factors driving myogenic differentiation arrest and proliferation.

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11
Pathophys.
1
Histopath.
5
Phenotypes
5
Hypotheses
3
Gaps
26
Pathograph
4
Genes
10
Medical Actions
3
Subtypes
2
Differentials
5
Datasets
1
Trials
4
Models
30
References
2
Deep Research
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Classifications

ICD-O Morphology
Sarcoma
Harrison's Part
ONCOLOGY HEMATOLOGY
◆

Subtypes

3
PAX3-FOXO1 Fusion-Positive
The most common and aggressive subtype, harboring the t(2;13)(q35;q14) translocation. Associated with older age at diagnosis, extremity primary sites, and inferior survival compared to other subtypes.
Show evidence (2 references)
PMID:39686893 SUPPORT Human Clinical
"According to literature data, the frequency of the PAX3::FOXO1 translocation is 70-90% and the PAX7::FOXO1 translocation 10-30%."
Supports PAX3-FOXO1 as the dominant fusion-positive subtype in alveolar rhabdomyosarcoma.
PMID:22454413 SUPPORT Human Clinical
"Among nonmetastatic patients, patients who were PAX3/FOXO1 positive had a significantly poorer outcome compared with both alveolar-negative and PAX7/FOXO1-positive patients."
Directly supports the poorer prognosis asserted for the PAX3-FOXO1 subtype relative to the other molecular groups.
PAX7-FOXO1 Fusion-Positive
Harbors the t(1;13)(p36;q14) translocation. This is the less common FOXO1-rearranged subtype and is generally associated with better prognosis than PAX3-FOXO1 positive tumors.
Show evidence (2 references)
PMID:39686893 SUPPORT Human Clinical
"According to literature data, the frequency of the PAX3::FOXO1 translocation is 70-90% and the PAX7::FOXO1 translocation 10-30%."
Supports PAX7-FOXO1 as a recurrent minority fusion-positive subtype in alveolar rhabdomyosarcoma.
PMID:22454413 SUPPORT Human Clinical
"Among nonmetastatic patients, patients who were PAX3/FOXO1 positive had a significantly poorer outcome compared with both alveolar-negative and PAX7/FOXO1-positive patients."
Supports the relative outcome distinction between PAX7-FOXO1-positive and PAX3-FOXO1-positive nonmetastatic disease.
Fusion-Negative Alveolar Rhabdomyosarcoma
Approximately 20% of histologically defined ARMS lack PAX-FOXO1 fusions. These tumors have clinical behavior and molecular features more similar to embryonal rhabdomyosarcoma.
Show evidence (1 reference)
PMID:39686893 SUPPORT Human Clinical
"Approximately 20% of cases of alveolar RMS do not have cytogenetic signs of rearrangements of the FOXO1 gene."
Directly supports the existence of fusion-negative ARMS at approximately 20% frequency.
◈

Mechanistic Hypotheses

5
Canonical PAX-FOXO1 Fusion Regulatory Program
canonical_fusion_regulatory_program CANONICAL
Evidence balance 1 support
PAX3/7-FOXO1 is the initiating molecular driver of fusion-positive ARMS and produces a fusion-dependent transcriptional and enhancer state that blocks myogenic differentiation and supports malignant behavior.
This hypothesis group is intentionally not a fully ordered linear chain. Edges from the fusion regulatory program to sibling outputs should be read as curated disease-model links supported at the current graph granularity, not as proof that all sibling outputs are causally upstream of one another.
Pathograph links
PAX-FOXO1 Fusion Oncogene -> PAX-FOXO1 Disease Enhancer Reprogramming DIRECT The fusion oncogene establishes an aberrant enhancer and super-enhancer transcriptional program that sits between the chromosomal fusion and phenotype-level outputs.
PAX-FOXO1 Disease Enhancer Reprogramming -> Blocked Myogenic Differentiation INDIRECT KNOWN INTERMEDIATES Fusion-driven enhancer reprogramming impairs the terminal skeletal muscle differentiation program. Intermediates: fusion-dependent transcriptional reprogramming; suppression of terminal myogenic differentiation programs
Show evidence (1 reference)
PMID:40508013 SUPPORT Other
"We discuss the central role of fusion proteins in transcriptional reprogramming, impaired myogenic differentiation, and super-enhancer activation."
Supports the canonical fusion-to-regulatory-program model used to group the core pathograph edges.
Chromatin-Cofactor and Protein-Stability Feedback Model
chromatin_feedback_maintenance_model EMERGING
Evidence balance 2 support
ETS1/KDM3A chromatin cofactor activity and YOD1/N-Myc protein-stability feedback are candidate maintenance mechanisms for the PAX3-FOXO1 regulatory state. They are not modeled as downstream consequences of measured open chromatin; they are candidate inputs or feedback arms that can be tested against a chromatin-state readout.
Current evidence supports biochemical interaction, chromatin occupancy, target-gene regulation, and growth effects. It does not yet fully resolve whether these mechanisms are required upstream of all disease-defining chromatin features, restricted to a subset of target loci, or partly downstream adaptive programs.
Pathograph links
PAX-FOXO1 Disease Enhancer Reprogramming -> ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module INDIRECT KNOWN INTERMEDIATES The fusion regulatory program induces ETS1 and intersects with KDM3A; this edge marks the entry into a feedback/cofactor module, not a claim that measured open chromatin causes the cofactor state. Intermediates: PAX3-FOXO1-dependent ETS1 induction; KDM3A-dependent ETS1 induction
PAX-FOXO1 Disease Enhancer Reprogramming -> YOD1-N-Myc PAX-FOXO1 Feedback Loop INDIRECT KNOWN INTERMEDIATES Fusion-driven transcription induces an N-Myc feedback state in which N-Myc also activates PAX-FOXO1 expression and complexes with the fusion protein. Intermediates: N-Myc induction downstream of PAX-FOXO1; reciprocal PAX3-FOXO1/N-Myc transcriptional activation
ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module -> PAX-FOXO1 Disease Enhancer Reprogramming DIRECT ETS1/KDM3A cofactor activity is modeled as a candidate maintenance input into the fusion-dependent enhancer program, not as a downstream consequence of the ATAC-seq accessibility measurement.
ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module -> FGFR-Driven RTK Signaling INDIRECT KNOWN INTERMEDIATES The cofactor module occupies and regulates disease-promoting enhancers including FGF8, which links the fusion/cofactor chromatin program to the FGF8/FGFR4 output branch. This does not by itself prove that FGFR signaling maintains the upstream chromatin state. Intermediates: PAX3-FOXO1/ETS1/KDM3A occupancy at the FGF8 enhancer; FGF8 expression in the FGFR4/FGF8 branch; FGFR4 phosphorylation in responsive fusion-positive RMS models
ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module -> Aberrant Cell Proliferation INDIRECT KNOWN INTERMEDIATES Disrupting the PAX3-FOXO1/ETS1 complex inhibits growth and invasive properties, implying that this cofactor module sustains malignant tumor cell behavior. Intermediates: PAX3-FOXO1/ETS1 complex disruption; reduced PAX3-FOXO1 chromatin occupancy; altered FGF8, IL4R, MEST, and PODXL expression
YOD1-N-Myc PAX-FOXO1 Feedback Loop -> PAX-FOXO1 Disease Enhancer Reprogramming INDIRECT KNOWN INTERMEDIATES Stabilizing PAX-FOXO1 and N-Myc is modeled as a feedback input into the fusion-dependent regulatory state. The cited work supports reciprocal transcriptional activation and malignancy dependence; whether the full ARMS open-chromatin signature collapses after YOD1 inhibition remains an explicit open test. Intermediates: YOD1-dependent PAX-FOXO1 and N-Myc protein stabilization; reciprocal PAX3-FOXO1/N-Myc transcriptional activation
YOD1-N-Myc PAX-FOXO1 Feedback Loop -> Aberrant Cell Proliferation INDIRECT KNOWN INTERMEDIATES YOD1-dependent stabilization of PAX-FOXO1 and N-Myc sustains FP-RMS growth. Intermediates: degradation of PAX-FOXO1 and N-Myc after YOD1 knockdown or inhibition; collapse of PAX3-FOXO1/N-Myc positive feedback
Show evidence (2 references)
PMID:39448867 SUPPORT In Vitro
"We show that ETS1, which is induced by both PAX3-FOXO1 and KDM3A, exists in complex with PAX3-FOXO1, and augments PAX3-FOXO1 chromatin occupancy."
Supports ETS1/KDM3A as a candidate chromatin-maintenance arm of the fusion-dependent regulatory model.
PMID:41401084 SUPPORT In Vitro
"The reciprocal transcriptional activation of PAX3-FOXO1 and N-Myc is critical for FP-RMS malignancy."
Supports the YOD1/N-Myc branch as a feedback-maintenance hypothesis rather than a simple downstream proliferation marker.
FGFR/FGF8 Downstream Output Dependency Model
fgfr_downstream_output_dependency_model EMERGING
Evidence balance 1 support
A subset of fusion-positive RMS shows high FGF8/FGFR4 expression, FGFR4 phosphorylation, and FGFR inhibitor response. This is modeled as a downstream output or branch dependency unless perturbation evidence shows that FGFR signaling feeds back to maintain the fusion chromatin state.
This grouping separates a druggable output branch from the core chromatin regulatory-state hypothesis. FGF8 enhancer occupancy supports a link to the fusion/cofactor program, while FGFR4 phosphorylation and inhibitor response support branch activity and therapeutic relevance.
Pathograph links
ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module -> FGFR-Driven RTK Signaling INDIRECT KNOWN INTERMEDIATES The cofactor module occupies and regulates disease-promoting enhancers including FGF8, which links the fusion/cofactor chromatin program to the FGF8/FGFR4 output branch. This does not by itself prove that FGFR signaling maintains the upstream chromatin state. Intermediates: PAX3-FOXO1/ETS1/KDM3A occupancy at the FGF8 enhancer; FGF8 expression in the FGFR4/FGF8 branch; FGFR4 phosphorylation in responsive fusion-positive RMS models
FGFR-Driven RTK Signaling -> RAS/PI3K Effector Pathway Activation INDIRECT KNOWN INTERMEDIATES FGFR4 signaling is curated as an RTK input to downstream RAS-MAPK and PI3K-AKT effector arms. The canonical receptor-to-effector mechanism is supported, while ARMS-specific dependence remains context-dependent. Intermediates: FRS2 phosphorylation; GRB2 adaptor recruitment
RAS/PI3K Effector Pathway Activation -> Aberrant Cell Proliferation INDIRECT KNOWN INTERMEDIATES RAS-MAPK and PI3K-AKT effector pathway activation is modeled as a pro-proliferative and survival output of the RTK/RAS/PIK3CA axis. The edge preserves pathograph connectivity but remains qualified: the cited ARMS/RMS evidence supports recurrent pathway involvement, not a direct or universal ARMS-specific causal step. Intermediates: MAPK-dependent cell-cycle entry; AKT-dependent survival signaling
Show evidence (1 reference)
PMID:42041178 SUPPORT Human Clinical
"We highlight the utility of FGFR inhibitors in PAX3-FOXO1 fusion-positive rhabdomyosarcomas (FP-RMS) characterized by high FGFR4 and FGF8 RNA expression levels and FGFR4 activation (FGFR4_pY)."
Supports a distinct FGFR4/FGF8 output branch in fusion-positive RMS.
HDAC3 Chemotherapy-Resistance Branch Model
therapy_resistance_branch_model EMERGING
Evidence balance 1 support
PAX3::FOXO1-mediated checkpoint adaptation and the HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit form a therapy-context resistance branch that contributes to relapse under chemotherapy pressure.
This group should not be conflated with the initiating ARMS regulatory program. It is a curated resistance branch that may affect chromatin state in resistant disease, but the cited evidence primarily supports chemotherapy-resistance biology.
Pathograph links
PAX-FOXO1 Disease Enhancer Reprogramming -> HDAC3-SMARCA4-miR-27a Chemotherapy Resistance Circuit INDIRECT KNOWN INTERMEDIATES PAX3::FOXO1-mediated cell-cycle checkpoint adaptation creates a treatment-resistance branch mediated by the HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit. Intermediates: PAX3::FOXO1-mediated cell-cycle checkpoint adaptation; HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit
HDAC3-SMARCA4-miR-27a Chemotherapy Resistance Circuit -> Chemotherapy Resistance and Relapse INDIRECT KNOWN INTERMEDIATES The HDAC3-linked checkpoint adaptation circuit permits tumor cells to survive cytotoxic treatment pressure and contributes to relapse. Intermediates: PAX3::FOXO1-mediated cell-cycle checkpoint adaptation; HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 resistance circuit; survival under cytotoxic chemotherapy pressure
Show evidence (1 reference)
PMID:39147820 SUPPORT Model Organism
"Chemotherapy resistance in ARMS has previously been attributed to PAX3::FOXO1-mediated cell cycle checkpoint adaptation, which is mediated by an HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit that can be disrupted by HDAC3 inhibition."
Supports the HDAC3 circuit as a chemotherapy-resistance branch linked to PAX3::FOXO1 biology.
Immune-Evasive and Fibroblast-Supported TME Model
microenvironment_support_model EMERGING
Evidence balance 1 support
Fusion-positive RMS can acquire an immune-cold and fibroblast-supported tumor microenvironment that promotes growth, migration, immune evasion, and chemotherapy resistance.
The evidence is strongest for fibroblast-supported growth and cyclophosphamide resistance in fusion-positive RMS models. The edge from fusion state to immune evasion remains broader and partially supported.
Pathograph links
PAX-FOXO1 Disease Enhancer Reprogramming -> Immune-Evasive Tumor Microenvironment INDIRECT UNKNOWN INTERMEDIATES Fusion oncogene activity contributes to reduced antigen presentation and immune-cell infiltration, creating an immune-evasive tumor state. Intermediates: altered antigen presentation; reduced immune-cell infiltration; specific fusion-regulated immune-evasion targets remain incompletely resolved
Immune-Evasive Tumor Microenvironment -> Aberrant Cell Proliferation DIRECT Cancer-associated fibroblast secreted factors support fusion-positive RMS tumor-cell growth, migration, and treatment resistance.
Immune-Evasive Tumor Microenvironment -> Chemotherapy Resistance and Relapse DIRECT Cancer-associated fibroblast support can add a microenvironmental treatment-resistance layer on top of tumor-cell-intrinsic resistance circuitry.
Immune-Evasive Tumor Microenvironment -> Metastatic Disease INDIRECT KNOWN INTERMEDIATES Fibroblast-supported migration is a plausible contributor to metastatic progression in fusion-positive RMS. The edge is deliberately indirect: the cited coculture study measures migration, while the clinical source establishes metastasis as a frequent outcome of the fusion-positive alveolar subtype. Intermediates: fibroblast-secreted promigratory factors; invasion and dissemination
Show evidence (1 reference)
PMID:41131073 SUPPORT In Vitro
"Compared to normal lung fibroblasts, these cancer-associated fibroblasts secreted distinct factors that specifically supported the growth and migration of fusion-positive rhabdomyosarcoma cells."
Supports the fibroblast-supported microenvironment model in fusion-positive RMS.
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Discussions and Knowledge Gaps

3
Which upstream or feedback-maintenance mechanism is required for the fusion-dependent regulatory program that produces the ARMS-specific open-chromatin signature, and can any chemical or genetic perturbation phenocopy acute fusion withdrawal at that assay readout?
KNOWLEDGE GAP OPEN gap_arms_pax_foxo1_dependency_hierarchy
Attached to
pathophysiology#PAX-FOXO1 Fusion Oncogene pathophysiology#PAX-FOXO1 Disease Enhancer Reprogramming pathophysiology#ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module pathophysiology#YOD1-N-Myc PAX-FOXO1 Feedback Loop pathophysiology#HDAC3-SMARCA4-miR-27a Chemotherapy Resistance Circuit pathophysiology#Chemotherapy Resistance and Relapse treatments#PAX-FOXO1/ETS1 Complex Disruption treatments#YOD1 Inhibition treatments#Histone Deacetylase Inhibitor Therapy
Older work established PAX3::FOXO1 and PAX7::FOXO1 as molecular drivers, but a 2025 therapy review still notes that standard systemic therapy remains VAC despite decades of fusion knowledge. The disease model now makes the hidden middle explicit but should not treat open chromatin as a causal node: open chromatin is the observable readout of a fusion-dependent regulatory program. The causal candidates are upstream or feedback-maintenance mechanisms such as PAX-FOXO1 protein abundance, ETS1/KDM3A cofactor occupancy, and YOD1/N-Myc stabilization. HDAC3-SMARCA4-miR-27a is better treated as a chemotherapy-resistance branch, and FGFR4/FGF8 signaling is better treated as a downstream output or feedback-control test, unless perturbation proves that either one feeds back onto the regulatory program. Forward curation through 2024-2026 provides partial therapeutic handles for those layers, but does not yet establish which handle changes the disease-defining regulatory state rather than only improving a downstream phenotype in one model context.
Proposed experiments
ARMS regulatory-state dependency screen using open chromatin as readout
isogenic dependency mapping experiment Relation: this experiment is of type this experiment type This experiment is of type isogenic dependency mapping experiment.
exp_arms_isogenic_pax_foxo1_dependency_prioritization
Define disease-specific open chromatin regions in matched FP-RMS models and use that signature as an assay readout, not as the causal mechanism. Perturb candidate causes of the fusion-dependent regulatory program first: acute PAX3-FOXO1 withdrawal, PAX3-FOXO1/ETS1 complex disruption, and YOD1 inhibition. Then use HDAC inhibition as a resistance-branch test under chemotherapy pressure and FGFR inhibition as a downstream-output control. Compare diagnostic-like, relapse-like, and chemotherapy-resistant states to determine which perturbation changes the regulatory-state readout and which only changes viability, signaling, or drug response downstream.
Model systems
FP-RMS cell-line and patient-derived culture panel
Human fusion-positive rhabdomyosarcoma models spanning PAX3-FOXO1 and PAX7-FOXO1 states, including diagnostic-like cultures and relapse- or chemotherapy-resistance-enriched cultures with matched baseline ATAC-seq or equivalent open-chromatin profiles.
CELL LINE PMID:41401084 link
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
skeletal muscle myoblast CL:0000515 Cell Ontology (CL) Relation: this experimental model uses this cell type This experimental model uses skeletal muscle myoblast (CL:0000515). CL:0000515 is a cell type from the Cell Ontology.
Perturbations
Acute PAX-FOXO1 withdrawal reference
pathophysiology#PAX-FOXO1 Fusion Oncogene
Degrade, silence, or inducibly withdraw the fusion protein to create the reference regulatory-state and open-chromatin-signature change for all downstream comparisons.
PAX-FOXO1/ETS1 complex disruption
treatments#PAX-FOXO1/ETS1 Complex Disruption
Apply YK-4-279-like complex disruption to test whether the ETS1/KDM3A cofactor handle collapses PAX-FOXO1 enhancer occupancy.
YOD1 feedback-loop inhibition
treatments#YOD1 Inhibition
Inhibit or knock down YOD1 to destabilize PAX-FOXO1 and N-Myc and test whether feedback-loop collapse changes the fusion-dependent regulatory program as measured by open chromatin and transcriptional readouts.
HDAC3 resistance-circuit inhibition
treatments#Histone Deacetylase Inhibitor Therapy
Treat with entinostat or a more selective HDAC3 perturbation during chemotherapy exposure to test whether a resistance-specific branch is reversed. This is not interpreted as baseline regulatory-state maintenance unless it also shifts the fusion-withdrawal-like ATAC and occupancy readouts.
FGFR pathway inhibition
treatments#FGFR Inhibitor Therapy
Inhibit FGFR4/FGF8 signaling as a downstream-output control. A viability or ERK/AKT response without an ATAC or fusion-occupancy shift would classify FGFR signaling as an output of the regulatory program rather than a maintainer of it.
Combination rescue matrix
pathophysiology#Chemotherapy Resistance and Relapse
Combine upstream/feedback regulatory-state perturbations with resistance-branch or downstream-output inhibitors to test whether chromatin-state rescue must be paired with suppression of resistant outgrowth.
Readouts
Disease-specific open chromatin signature change
pathophysiology#PAX-FOXO1 Disease Enhancer Reprogramming
Measure whether disease-specific ATAC-seq peaks and enhancer activity shift toward the acute fusion-withdrawal or fusion-negative comparator state after each perturbation. The ATAC-seq peaks are the observable signature used to infer regulatory-state change, not a separate causal node in the pathograph.
chromatin remodeling GO:0006338 Gene Ontology (GO) Relation: this readout reports on this biological process This readout reports on chromatin remodeling (GO:0006338). GO:0006338 is a biological process from the Gene Ontology. positive regulation of transcription by RNA polymerase II GO:0045944 Gene Ontology (GO) Relation: this readout reports on this biological process This readout reports on positive regulation of transcription by RNA polymerase II (GO:0045944). GO:0045944 is a biological process from the Gene Ontology.
ATAC-seq Relation: this readout is measured by this assay This readout is measured by ATAC-seq. CUT&Tag Relation: this readout is measured by this assay This readout is measured by CUT&Tag. single-cell RNA-seq Relation: this readout is measured by this assay This readout is measured by single-cell RNA-seq.
Direction: NEGATIVE
Fusion occupancy and mechanism-specific target output
pathophysiology#ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module
Quantify PAX-FOXO1 and ETS1 occupancy, FGF8/IL4R/MEST/PODXL expression, MYCN/N-Myc expression, YOD1-dependent protein abundance, and HDAC3-resistance-circuit markers after each perturbation to distinguish causal regulatory-state change from downstream output change.
positive regulation of transcription by RNA polymerase II GO:0045944 Gene Ontology (GO) Relation: this readout reports on this biological process This readout reports on positive regulation of transcription by RNA polymerase II (GO:0045944). GO:0045944 is a biological process from the Gene Ontology.
CUT&Tag Relation: this readout is measured by this assay This readout is measured by CUT&Tag. RNA sequencing Relation: this readout is measured by this assay This readout is measured by RNA sequencing. immunoblot Relation: this readout is measured by this assay This readout is measured by immunoblot.
Direction: NEGATIVE
Differentiation and malignant-growth response
pathophysiology#Blocked Myogenic Differentiation
Measure myogenic differentiation, proliferation, apoptosis, and invasive properties after each regulatory-state perturbation or downstream-output control.
cell differentiation GO:0030154 Gene Ontology (GO) Relation: this readout reports on this biological process This readout reports on cell differentiation (GO:0030154). GO:0030154 is a biological process from the Gene Ontology.
differentiation assay Relation: this readout is measured by this assay This readout is measured by differentiation assay. cell viability assay Relation: this readout is measured by this assay This readout is measured by cell viability assay. invasion assay Relation: this readout is measured by this assay This readout is measured by invasion assay.
Direction: POSITIVE
Chemotherapy-resistance reversal
pathophysiology#Chemotherapy Resistance and Relapse
Quantify whether regulatory-state changes or HDAC3 resistance-branch inhibition predict improved chemotherapy sensitivity and suppression of resistant outgrowth in relapse-like models.
response to xenobiotic stimulus GO:0009410 Gene Ontology (GO) Relation: this readout reports on this biological process This readout reports on response to xenobiotic stimulus (GO:0009410). GO:0009410 is a biological process from the Gene Ontology.
cell viability assay Relation: this readout is measured by this assay This readout is measured by cell viability assay. chemotherapy response assay Relation: this readout is measured by this assay This readout is measured by chemotherapy response assay.
Direction: NEGATIVE
Controls
Fusion-negative RMS comparator
Tests whether perturbation effects are specific to PAX-FOXO1-driven disease.
Acute fusion-withdrawal positive control
Defines the expected full chromatin-collapse signature for a fusion-dependent state.
Vehicle or non-targeting perturbation controls
Baseline control for drug, degron, or genetic perturbation effects.
Decision criterion
A mechanism is classified as regulatory-state-maintaining if its chemical or genetic perturbation reproducibly shifts the ARMS-specific open chromatin signature and fusion/cofactor occupancy toward the acute fusion-withdrawal reference, then produces coherent downstream effects on differentiation, proliferation or invasion, and chemotherapy response. A perturbation that improves viability, signaling, or chemotherapy response without changing the open-chromatin and occupancy readouts is classified as a downstream or branch-specific therapeutic handle, not as closure of the core regulatory-state gap.
Would support
pathophysiology#PAX-FOXO1 Fusion Oncogene pathophysiology#PAX-FOXO1 Disease Enhancer Reprogramming pathophysiology#ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module pathophysiology#YOD1-N-Myc PAX-FOXO1 Feedback Loop pathophysiology#HDAC3-SMARCA4-miR-27a Chemotherapy Resistance Circuit pathophysiology#Chemotherapy Resistance and Relapse pathophysiology#Blocked Myogenic Differentiation pathophysiology#Aberrant Cell Proliferation
Show evidence (3 references)
PMID:41401084 SUPPORT Model Organism
"The reciprocal transcriptional activation of PAX3-FOXO1 and N-Myc is critical for FP-RMS malignancy."
Supports inclusion of the YOD1/N-Myc feedback arm in the proposed dependency-prioritization experiment.
PMID:39448867 SUPPORT In Vitro
"We further show that the PAX3-FOXO1/ETS1 complex can be disrupted by the clinically relevant small molecule inhibitor YK-4-279."
Supports inclusion of ETS1-dependent fusion chromatin occupancy as a candidate targetable dependency layer.
+ 1 more reference
Show evidence (3 references)
PMID:41038289 SUPPORT Other
"Although the gene fusions PAX3::FOXO1 and PAX7::FOXO1 were discovered in the early 1990s, and since that time shown to be the molecular drivers of the disease, the best treatment to date still remains VAC (vincristine, actinomycin D, cyclophosphamide) combination therapy, first instituted as..."
Shows that the therapy gap remains open despite longstanding knowledge of the causal fusion oncogenes.
PMID:41401084 SUPPORT Model Organism
"However, the oncogenic mechanisms and therapeutic strategies of PAX-FOXO1 remain incompletely understood."
Explicitly states that PAX-FOXO1 mechanisms and therapeutic strategies remain incomplete while presenting one forward partial answer.
PMID:39448867 SUPPORT In Vitro
"However, details of PAX3-FOXO1 epigenetic mechanisms, including interactions with, and dependence on, other chromatin and transcription factors, are incompletely understood."
Documents that cofactor-dependent fusion chromatin regulation remains an open mechanistic layer even after recent target-discovery work.
Which fusion-positive ARMS tumors have disease-specific open chromatin at FGF8 regulatory elements that correspond to previously reported PAX3-FOXO1/ETS1/KDM3A-bound enhancers of FGF8, and also show high FGF8 RNA, high FGFR4 RNA, and FGFR4 phosphorylation, such that the tumor is clinically responsive to FGFR inhibition? Conversely, which tumors express some of the FGF8/FGFR4/FGFR4_pY signature but are not FGFR-dependent because downstream RAS/PI3K activation, relapse-associated adaptation, or other resistance circuitry bypasses FGFR signaling?
KNOWLEDGE GAP OPEN gap_arms_fgfr_response_biomarkers
Attached to
pathophysiology#PAX-FOXO1 Fusion Oncogene pathophysiology#PAX-FOXO1 Disease Enhancer Reprogramming pathophysiology#ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module pathophysiology#FGFR-Driven RTK Signaling pathophysiology#RAS/PI3K Effector Pathway Activation treatments#FGFR Inhibitor Therapy
Recent 2026 multiplatform profiling provides the strongest forward evidence that FGFR4/FGF8 coexpression with FGFR4 phosphorylation can identify FGFR-inhibitor-sensitive FP-RMS. The same paper frames the broader unresolved question: RNA overexpression alone is common, but it is not always clear when receptor expression marks kinase activation, signaling dependence, and drug response. Because the pathograph now connects FGF8 to the ETS1/KDM3A/PAX-FOXO1 chromatin cofactor module, the open curation problem is whether disease-specific open chromatin at FGF8 regulatory elements that correspond to PAX3-FOXO1/ETS1/KDM3A-bound enhancers of FGF8, direct factor-occupancy evidence where available, FGF8/FGFR4 transcript abundance, FGFR4 phosphorylation, and drug response form one coherent dependency signature or split into bypass states.
Proposed experiments
Functional FGFR biomarker-response panel in FP-RMS
functional precision-oncology biomarker experiment Relation: this experiment is of type this experiment type This experiment is of type functional precision-oncology biomarker experiment.
exp_arms_fgfr_functional_biomarker_response_panel
Assemble FP-RMS patient samples, cell lines, organoids, and PDX-derived cultures stratified by ATAC-seq accessibility at FGF8 regulatory elements that correspond to PAX3-FOXO1/ETS1/KDM3A-bound enhancers of FGF8, by direct PAX3-FOXO1/ETS1/KDM3A occupancy where factor-binding data are available, by FGFR4 RNA, FGF8 RNA, FGFR4 phosphorylation, and RTK/RAS/PI3K alterations. Test FGFR4-selective and multikinase FGFR inhibitors alone and with downstream pathway blockade to determine which biomarker combinations predict response or bypass.
Model systems
FP-RMS phosphoproteomic response panel
Human fusion-positive rhabdomyosarcoma samples and derived models with matched transcriptomic, phosphoproteomic, genomic, and drug-response measurements.
OTHER PMID:42041178 link
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Perturbations
FGFR inhibitor challenge
treatments#FGFR Inhibitor Therapy
Treat models with FGFR4-selective and multikinase FGFR inhibitors to compare response across FGFR4 RNA, FGF8 RNA, and FGFR4_pY strata.
Downstream bypass testing
pathophysiology#RAS/PI3K Effector Pathway Activation
Add RAS-MAPK or PI3K-AKT pathway blockade, or analyze models with existing RTK/RAS/PI3K alterations, to identify FGFR-independent resistance states.
Readouts
FGF8 fusion/cofactor regulatory state and FGFR response
pathophysiology#ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module
Quantify disease-specific open chromatin at FGF8 regulatory elements that correspond to PAX3-FOXO1/ETS1/KDM3A-bound enhancers of FGF8, and, where possible, separately quantify PAX3-FOXO1, ETS1, and KDM3A occupancy. Relate those chromatin-accessibility and factor-occupancy features to FGF8 RNA, FGFR4 RNA, and FGFR4 phosphorylation.
chromatin remodeling GO:0006338 Gene Ontology (GO) Relation: this readout reports on this biological process This readout reports on chromatin remodeling (GO:0006338). GO:0006338 is a biological process from the Gene Ontology.
ATAC-seq Relation: this readout is measured by this assay This readout is measured by ATAC-seq. CUT&Tag Relation: this readout is measured by this assay This readout is measured by CUT&Tag. RNA sequencing Relation: this readout is measured by this assay This readout is measured by RNA sequencing.
Direction: NEGATIVE
FGFR activation and signaling dependence
pathophysiology#FGFR-Driven RTK Signaling
Quantify FGFR4 phosphorylation, FGF8/FGFR4 RNA, downstream ERK/AKT signaling, and suppression of pathway output after FGFR inhibition.
fibroblast growth factor receptor signaling pathway GO:0008543 Gene Ontology (GO) Relation: this readout reports on this biological process This readout reports on fibroblast growth factor receptor signaling pathway (GO:0008543). GO:0008543 is a biological process from the Gene Ontology.
phosphoproteomics Relation: this readout is measured by this assay This readout is measured by phosphoproteomics. RNA sequencing Relation: this readout is measured by this assay This readout is measured by RNA sequencing.
Direction: NEGATIVE
Drug response and bypass
treatments#FGFR Inhibitor Therapy
Measure tumor growth, viability, apoptosis, and pathway reactivation after FGFR inhibition alone or with downstream blockade.
cell viability assay Relation: this readout is measured by this assay This readout is measured by cell viability assay. tumor growth assay Relation: this readout is measured by this assay This readout is measured by tumor growth assay.
Direction: NEGATIVE
Controls
FGFR4-low FP-RMS controls
Models lacking the candidate FGFR4/FGF8/FGFR4_pY response signature.
RAS/PI3K-altered comparator models
Models expected to bypass upstream FGFR dependence.
Decision criterion
The biomarker model is supported if disease-specific open chromatin at FGF8 regulatory elements corresponding to PAX3-FOXO1/ETS1/KDM3A-bound enhancers of FGF8, direct PAX3-FOXO1/ETS1/KDM3A occupancy where measured, high FGF8/FGFR4 RNA, and FGFR4 phosphorylation jointly predict FGFR-inhibitor response and pathway suppression, while discordant, RAS/PI3K-altered, or relapse/resistance-enriched models show bypass or require combination downstream blockade.
Would support
pathophysiology#ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module pathophysiology#FGFR-Driven RTK Signaling treatments#FGFR Inhibitor Therapy
Would refute
pathophysiology#FGFR-Driven RTK Signaling
Show evidence (1 reference)
PMID:42041178 SUPPORT Model Organism
"We demonstrate marked tumor growth inhibition in all FP-RMS PDXs treated with single-agent FGF401 (FGFR4-specific inhibitor) and single-agent lenvatinib (multikinase FGFR inhibitor)"
Provides the functional precedent for testing FGFR response biomarkers across a broader FP-RMS model panel.
Show evidence (2 references)
PMID:42041178 SUPPORT Human Clinical
"A major obstacle preventing further advances and clinical implementation is the lack of predictive response biomarkers to guide TK-targeted treatments."
Explicitly identifies predictive response biomarkers as an active barrier to tyrosine-kinase-targeted therapy implementation.
PMID:42041178 SUPPORT Human Clinical
"The unresolved question is when upregulated TK expression is associated with kinase activation and signaling dependence."
Defines the specific mechanistic and biomarker gap that applies to FGFR4/FGF8-high fusion-positive RMS.
In fusion-positive ARMS, is immunotherapy resistance driven by a fusion/enhancer-imposed immune-cold chromatin state, antigen heterogeneity, cancer-associated fibroblast checkpoint/cytokine support, or a combined tumor-intrinsic and microenvironmental resistance state?
KNOWLEDGE GAP OPEN gap_arms_tme_immunotherapy_resistance
Attached to
pathophysiology#PAX-FOXO1 Fusion Oncogene pathophysiology#PAX-FOXO1 Disease Enhancer Reprogramming pathophysiology#Immune-Evasive Tumor Microenvironment pathophysiology#Chemotherapy Resistance and Relapse pathophysiology#Aberrant Cell Proliferation
Recent immunotherapy and tumor-microenvironment papers make the gap more specific than "immunotherapy has not worked." CAR-T reviews identify limited clinical activity and hurdles such as antigen heterogeneity and immunosuppressive microenvironments; tumor-immune reviews connect PAX3:FOXO1 to reduced antigen presentation and immune infiltration; and a 2025 fusion-positive RMS fibroblast model shows immune-checkpoint and cyclophosphamide-resistance effects. With the fusion/enhancer node now explicit, the remaining gap is whether immune resistance is encoded in the tumor-cell chromatin state, imposed by CAF-supported microenvironmental signaling, or produced by both layers together.
Proposed experiments
FP-RMS tumor-CAF-immune coculture resistance panel
tumor microenvironment immunotherapy resistance experiment Relation: this experiment is of type this experiment type This experiment is of type tumor microenvironment immunotherapy resistance experiment.
exp_arms_tme_coculture_immunotherapy_resistance_panel
Build human FP-RMS tumor-cell, cancer-associated fibroblast, and immune cocultures with matched antigen-expression, cytokine, single-cell transcriptomic, and open-chromatin profiling. Test CAR-T targets, checkpoint blockade, CXCR4 inhibition, CAF depletion, and fusion/enhancer perturbation to distinguish antigen-loss, tumor-intrinsic immune-cold chromatin, immune-exclusion, and fibroblast-mediated resistance mechanisms.
Model systems
FP-RMS tumor-CAF-immune coculture
Human fusion-positive rhabdomyosarcoma tumor cells cocultured with patient-derived or metastatic-site cancer-associated fibroblasts and T cells.
CO CULTURE PMID:41131073 link
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
cancer-associated fibroblast CL:0000057 Cell Ontology (CL) Relation: this experimental model uses this cell type This experimental model uses cancer-associated fibroblast, annotated with fibroblast (CL:0000057). CL:0000057 is a cell type from the Cell Ontology. T cell CL:0000084 Cell Ontology (CL) Relation: this experimental model uses this cell type This experimental model uses T cell (CL:0000084). CL:0000084 is a cell type from the Cell Ontology.
Perturbations
CAR-T and checkpoint intervention
pathophysiology#Immune-Evasive Tumor Microenvironment
Compare single-antigen and dual-antigen CAR-T approaches with checkpoint blockade in the presence and absence of fibroblast-conditioned microenvironmental support.
CAF/CXCR4-axis disruption
pathophysiology#Immune-Evasive Tumor Microenvironment
Deplete fibroblasts or inhibit CXCR4-linked signaling to test whether CAF-derived factors drive immune evasion and chemotherapy resistance.
Fusion/enhancer-state perturbation
pathophysiology#PAX-FOXO1 Disease Enhancer Reprogramming
Perturb the fusion/enhancer program with fusion withdrawal or selected chromatin-handle interventions to test whether antigen presentation and T-cell killing can be restored from the tumor-cell side.
Readouts
Antigen-presentation chromatin and immune infiltration state
pathophysiology#Immune-Evasive Tumor Microenvironment
Measure open chromatin and expression at antigen-presentation and immune-response programs, target-antigen expression, T-cell killing, immune-checkpoint expression, cytokines, and tumor-cell survival after immunotherapy challenge.
antigen processing and presentation GO:0019882 Gene Ontology (GO) Relation: this readout reports on this biological process This readout reports on antigen processing and presentation (GO:0019882). GO:0019882 is a biological process from the Gene Ontology. immune response GO:0006955 Gene Ontology (GO) Relation: this readout reports on this biological process This readout reports on immune response (GO:0006955). GO:0006955 is a biological process from the Gene Ontology.
ATAC-seq Relation: this readout is measured by this assay This readout is measured by ATAC-seq. single-cell RNA-seq Relation: this readout is measured by this assay This readout is measured by single-cell RNA-seq. flow cytometry Relation: this readout is measured by this assay This readout is measured by flow cytometry. cytokine profiling Relation: this readout is measured by this assay This readout is measured by cytokine profiling. cell killing assay Relation: this readout is measured by this assay This readout is measured by cell killing assay.
Direction: POSITIVE
Chemotherapy and immunotherapy resistance
pathophysiology#Immune-Evasive Tumor Microenvironment
Quantify cyclophosphamide sensitivity, CAR-T cytotoxicity, checkpoint response, and rescue by CAF/CXCR4-axis perturbation.
cell viability assay Relation: this readout is measured by this assay This readout is measured by cell viability assay. cytotoxicity assay Relation: this readout is measured by this assay This readout is measured by cytotoxicity assay.
Direction: NEGATIVE
Controls
Tumor-only and normal fibroblast coculture controls
Separates CAF-specific effects from generic stromal support.
Antigen-negative CAR-T control
Controls for nonspecific T-cell activation or cytotoxicity.
Decision criterion
A resistance mechanism is prioritized if its perturbation restores antigen-presentation chromatin or expression, improves T-cell killing, and improves chemotherapy or immunotherapy response in CAF-supported FP-RMS cultures, while tumor-only, normal-fibroblast, or fusion-negative controls lack the same resistance phenotype.
Would support
pathophysiology#PAX-FOXO1 Disease Enhancer Reprogramming pathophysiology#Immune-Evasive Tumor Microenvironment
Would refute
pathophysiology#Immune-Evasive Tumor Microenvironment
Show evidence (2 references)
PMID:41131073 SUPPORT In Vitro
"This study establishes a model of cancer-associated fibroblasts from metastatic fusion-positive rhabdomyosarcoma."
Supports feasibility of the proposed FP-RMS CAF coculture model system.
PMID:41709231 SUPPORT Other
"Significant clinical hurdles include antigen heterogeneity, immunosuppressive tumor microenvironments, and logistical barriers in manufacturing."
Supports testing antigen heterogeneity and immunosuppressive TME as explicit resistance mechanisms for CAR-T strategies.
Show evidence (3 references)
PMID:41709231 SUPPORT Other
"While preclinical studies are promising, antitumor activity in clinical studies to date has been limited."
Establishes that immunotherapy resistance remains clinically relevant despite preclinical CAR-T promise.
PMID:41007114 SUPPORT Other
"pediatric RMS typically exhibits a "cold" immune profile, characterized by minimal T-cell infiltration, a low mutational burden, and resistance to immune checkpoint blockade."
Supports an immune-cold pediatric RMS context that may contribute to poor checkpoint response, while remaining broader than ARMS-only.
PMID:41131073 SUPPORT In Vitro
"Altogether, our results describe tumor-promoting mechanisms of growth, migration, and treatment resistance supported by the tumor microenvironment"
Supports a direct FP-RMS microenvironmental resistance mechanism that the proposed experiment should dissect.
⚙

Pathophysiology

11
PAX-FOXO1 Fusion Oncogene
The t(2;13) or t(1;13) translocations fuse the DNA-binding domain of PAX3 or PAX7 with the transactivation domain of FOXO1. The resulting fusion protein functions as a potent aberrant transcription factor that activates PAX target genes to supraphysiological levels, driving proliferation while blocking terminal myogenic differentiation.
Canonical PAX-FOXO1 Fusion Regulatory Program
skeletal muscle myoblast CL:0000515 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves skeletal muscle myoblast (CL:0000515). CL:0000515 is a cell type from the Cell Ontology.
PAX3 hgnc:8617 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves PAX3 (hgnc:8617). hgnc:8617 is a gene from the HUGO Gene Nomenclature Committee. PAX7 hgnc:8621 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves PAX7 (hgnc:8621). hgnc:8621 is a gene from the HUGO Gene Nomenclature Committee. FOXO1 hgnc:3819 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves FOXO1 (hgnc:3819). hgnc:3819 is a gene from the HUGO Gene Nomenclature Committee.
positive regulation of transcription by RNA polymerase II GO:0045944 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal positive regulation of transcription by RNA polymerase II (GO:0045944). GO:0045944 is a biological process from the Gene Ontology. ⚠ ABNORMAL
skeletal muscle tissue UBERON:0001134 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in skeletal muscle tissue (UBERON:0001134). UBERON:0001134 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
PAX-FOXO1 Disease Enhancer Reprogramming The fusion oncogene establishes an aberrant enhancer and super-enhancer transcriptional program that sits between the chromosomal fusion and phenotype-level outputs. Canonical PAX-FOXO1 Fusion Regulatory Program
Show evidence (2 references)
PMID:39686893 SUPPORT Human Clinical
"According to literature data, the frequency of the PAX3::FOXO1 translocation is 70-90% and the PAX7::FOXO1 translocation 10-30%."
Supports the prevalence of PAX3/7-FOXO1 fusions in alveolar rhabdomyosarcoma.
PMID:24436047 SUPPORT Human Clinical
"As expected, the defining genomic alteration seen across the entire cohort was recurrent t(2;13) or t(1;13), that resulted in a fusion of the N-terminus of PAX3 or PAX7 to the C-terminus of FOXO1"
Directly supports the translocation structure and resulting PAX-FOXO1 fusion in human RMS tumors.
PAX-FOXO1 Disease Enhancer Reprogramming
PAX-FOXO1 does not act as a generic "oncogene" in the pathograph; it rewires chromatin occupancy, enhancer activity, and transcriptional output. This node is the inferred regulatory program, not the ATAC-seq/open chromatin measurement itself. Disease-specific open chromatin is an assayable projection of this program and can be used to test whether perturbing candidate maintenance machinery changes the regulatory state itself, as opposed to changing downstream or branch-specific outputs such as FGFR signaling, immune evasion, or chemotherapy resistance.
Canonical PAX-FOXO1 Fusion Regulatory Program Chromatin-Cofactor and Protein-Stability Feedback Model HDAC3 Chemotherapy-Resistance Branch Model Immune-Evasive and Fibroblast-Supported TME Model
skeletal muscle myoblast CL:0000515 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves skeletal muscle myoblast (CL:0000515). CL:0000515 is a cell type from the Cell Ontology.
chromatin remodeling GO:0006338 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal chromatin remodeling (GO:0006338). GO:0006338 is a biological process from the Gene Ontology. ⚠ ABNORMAL positive regulation of gene expression GO:0010628 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal positive regulation of gene expression (GO:0010628). GO:0010628 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Downstream
ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module The fusion regulatory program induces ETS1 and intersects with KDM3A; this edge marks the entry into a feedback/cofactor module, not a claim that measured open chromatin causes the cofactor state. Chromatin-Cofactor and Protein-Stability Feedback Model
YOD1-N-Myc PAX-FOXO1 Feedback Loop Fusion-driven transcription induces an N-Myc feedback state in which N-Myc also activates PAX-FOXO1 expression and complexes with the fusion protein. Chromatin-Cofactor and Protein-Stability Feedback Model
HDAC3-SMARCA4-miR-27a Chemotherapy Resistance Circuit PAX3::FOXO1-mediated cell-cycle checkpoint adaptation creates a treatment-resistance branch mediated by the HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit. HDAC3 Chemotherapy-Resistance Branch Model
Blocked Myogenic Differentiation Fusion-driven enhancer reprogramming impairs the terminal skeletal muscle differentiation program. Canonical PAX-FOXO1 Fusion Regulatory Program
Immune-Evasive Tumor Microenvironment Fusion oncogene activity contributes to reduced antigen presentation and immune-cell infiltration, creating an immune-evasive tumor state. Immune-Evasive and Fibroblast-Supported TME Model
Show evidence (1 reference)
PMID:40508013 SUPPORT Other
"We discuss the central role of fusion proteins in transcriptional reprogramming, impaired myogenic differentiation, and super-enhancer activation."
Establishes transcriptional reprogramming and super-enhancer activation as central mechanisms in ARMS.
ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module
KDM3A and ETS1 form a disease-promoting chromatin cofactor axis with PAX3-FOXO1. ETS1 is induced by PAX3-FOXO1 and KDM3A, complexes with PAX3-FOXO1, augments fusion occupancy at enhancers, and helps maintain disease-promoting target genes including FGF8, IL4R, MEST, and PODXL. This is a direct mechanistic handle because YK-4-279 disrupts the PAX3-FOXO1/ETS1 complex and displaces PAX3-FOXO1 from chromatin.
Chromatin-Cofactor and Protein-Stability Feedback Model FGFR/FGF8 Downstream Output Dependency Model
chromatin remodeling GO:0006338 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal chromatin remodeling (GO:0006338). GO:0006338 is a biological process from the Gene Ontology. ⚠ ABNORMAL positive regulation of gene expression GO:0010628 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal positive regulation of gene expression (GO:0010628). GO:0010628 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Downstream
PAX-FOXO1 Disease Enhancer Reprogramming ETS1/KDM3A cofactor activity is modeled as a candidate maintenance input into the fusion-dependent enhancer program, not as a downstream consequence of the ATAC-seq accessibility measurement. Chromatin-Cofactor and Protein-Stability Feedback Model
FGFR-Driven RTK Signaling The cofactor module occupies and regulates disease-promoting enhancers including FGF8, which links the fusion/cofactor chromatin program to the FGF8/FGFR4 output branch. This does not by itself prove that FGFR signaling maintains the upstream chromatin state. Chromatin-Cofactor and Protein-Stability Feedback Model FGFR/FGF8 Downstream Output Dependency Model
Aberrant Cell Proliferation Disrupting the PAX3-FOXO1/ETS1 complex inhibits growth and invasive properties, implying that this cofactor module sustains malignant tumor cell behavior. Chromatin-Cofactor and Protein-Stability Feedback Model
Show evidence (1 reference)
PMID:39448867 SUPPORT In Vitro
"We show that ETS1, which is induced by both PAX3-FOXO1 and KDM3A, exists in complex with PAX3-FOXO1, and augments PAX3-FOXO1 chromatin occupancy."
Directly supports ETS1 as a PAX3-FOXO1 chromatin cofactor in fusion-positive RMS.
YOD1-N-Myc PAX-FOXO1 Feedback Loop
N-Myc is both a downstream target and a reciprocal activator of PAX-FOXO1. YOD1 stabilizes both PAX-FOXO1 and N-Myc, maintaining a positive feedback loop that amplifies oncogenic signaling. This creates a second targetable handle upstream of generic proliferation: destabilize the two oncogenic proteins together rather than treating N-Myc as only a downstream proliferation marker.
Chromatin-Cofactor and Protein-Stability Feedback Model
MYCN hgnc:7559 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves MYCN (hgnc:7559). hgnc:7559 is a gene from the HUGO Gene Nomenclature Committee.
protein stabilization GO:0050821 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased protein stabilization (GO:0050821). GO:0050821 is a biological process from the Gene Ontology. ↑ INCREASED positive regulation of gene expression GO:0010628 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased positive regulation of gene expression (GO:0010628). GO:0010628 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
PAX-FOXO1 Disease Enhancer Reprogramming Stabilizing PAX-FOXO1 and N-Myc is modeled as a feedback input into the fusion-dependent regulatory state. The cited work supports reciprocal transcriptional activation and malignancy dependence; whether the full ARMS open-chromatin signature collapses after YOD1 inhibition remains an explicit open test. Chromatin-Cofactor and Protein-Stability Feedback Model
Aberrant Cell Proliferation YOD1-dependent stabilization of PAX-FOXO1 and N-Myc sustains FP-RMS growth. Chromatin-Cofactor and Protein-Stability Feedback Model
Show evidence (1 reference)
PMID:41401084 SUPPORT In Vitro
"We further identified YOD1 as a deubiquitinating enzyme that stabilizes both PAX-FOXO1 and N-Myc."
Identifies YOD1 as the stabilizing enzyme for both members of the PAX-FOXO1/N-Myc feedback loop.
HDAC3-SMARCA4-miR-27a Chemotherapy Resistance Circuit
PAX3::FOXO1-mediated cell-cycle checkpoint adaptation creates a relapse and chemotherapy-resistance branch mediated by an HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit. This is the mechanistic target of HDAC3-directed epigenetic therapy with entinostat-like class I HDAC inhibition, not merely a generic "HDAC inhibitor" rationale.
HDAC3 Chemotherapy-Resistance Branch Model
regulation of cell cycle GO:0051726 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal regulation of cell cycle (GO:0051726). GO:0051726 is a biological process from the Gene Ontology. ⚠ ABNORMAL epigenetic regulation of gene expression GO:0040029 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal epigenetic regulation of gene expression (GO:0040029). GO:0040029 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Downstream
Chemotherapy Resistance and Relapse The HDAC3-linked checkpoint adaptation circuit permits tumor cells to survive cytotoxic treatment pressure and contributes to relapse. HDAC3 Chemotherapy-Resistance Branch Model
Show evidence (1 reference)
PMID:39147820 SUPPORT Model Organism
"Chemotherapy resistance in ARMS has previously been attributed to PAX3::FOXO1-mediated cell cycle checkpoint adaptation, which is mediated by an HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit that can be disrupted by HDAC3 inhibition."
Defines the HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 resistance circuit and its therapeutic vulnerability to HDAC3 inhibition.
Chemotherapy Resistance and Relapse
A clinically important disease state in which initially chemotherapy- responsive PAX3::FOXO1-positive ARMS survives treatment pressure, relapses, and becomes resistant. In this pathograph it is modeled as a downstream output of specific mechanisms, especially the HDAC3-SMARCA4-miR-27a checkpoint-adaptation circuit and microenvironmental support, rather than as an unexplained late clinical outcome.
response to xenobiotic stimulus GO:0009410 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal response to xenobiotic stimulus (GO:0009410). GO:0009410 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Show evidence (1 reference)
PMID:39147820 SUPPORT Other
"Metastatic PAX3::FOXO1+ ARMS often responds to chemotherapies initially, only to subsequently relapse and become resistant with most patients failing to survive beyond 8 years post-diagnosis."
Supports relapse and acquired chemotherapy resistance as a core clinical disease state in metastatic PAX3::FOXO1-positive ARMS.
FGFR-Driven RTK Signaling
One branch of the fusion-positive ARMS program is receptor tyrosine kinase signaling centered on FGFR4, driven by high FGFR4 and FGF8 expression and FGFR4 phosphoactivation. This is a directly druggable downstream output branch, not currently a proven maintainer of the upstream fusion-dependent chromatin state.
FGFR/FGF8 Downstream Output Dependency Model
fibroblast growth factor receptor signaling pathway GO:0008543 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased fibroblast growth factor receptor signaling pathway (GO:0008543). GO:0008543 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
RAS/PI3K Effector Pathway Activation FGFR4 signaling is curated as an RTK input to downstream RAS-MAPK and PI3K-AKT effector arms. The canonical receptor-to-effector mechanism is supported, while ARMS-specific dependence remains context-dependent. FGFR/FGF8 Downstream Output Dependency Model
Show evidence (1 reference)
PMID:42041178 SUPPORT Human Clinical
"We highlight the utility of FGFR inhibitors in PAX3-FOXO1 fusion-positive rhabdomyosarcomas (FP-RMS) characterized by high FGFR4 and FGF8 RNA expression levels and FGFR4 activation (FGFR4_pY)."
Patient and PDX profiling documents FGFR4 activation as a distinct, directly actionable receptor tyrosine kinase input in fusion-positive rhabdomyosarcoma.
RAS/PI3K Effector Pathway Activation
Receptor tyrosine kinase input converges on the downstream RAS-MAPK and PI3K-AKT effector pathways. Genomic profiling shows the combined RTK/RAS/PIK3CA axis is altered in the large majority of rhabdomyosarcomas; this effector branch is therefore a curated downstream signaling state, not a claim that RAS/PI3K activation is the only or universal route to ARMS proliferation.
FGFR/FGF8 Downstream Output Dependency Model
Ras protein signal transduction GO:0007265 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased Ras protein signal transduction (GO:0007265). GO:0007265 is a biological process from the Gene Ontology. ↑ INCREASED PI3K/AKT signal transduction GO:0043491 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased PI3K/AKT signal transduction, annotated with phosphatidylinositol 3-kinase/protein kinase B signal transduction (GO:0043491). GO:0043491 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Aberrant Cell Proliferation RAS-MAPK and PI3K-AKT effector pathway activation is modeled as a pro-proliferative and survival output of the RTK/RAS/PIK3CA axis. The edge preserves pathograph connectivity but remains qualified: the cited ARMS/RMS evidence supports recurrent pathway involvement, not a direct or universal ARMS-specific causal step. FGFR/FGF8 Downstream Output Dependency Model
Show evidence (1 reference)
PMID:24436047 SUPPORT Human Clinical
"Furthermore, alteration of the receptor tyrosine kinase/RAS/PIK3CA axis affects 93% of cases, providing a framework for genomics-directed therapies that might improve outcomes for patients with rhabdomyosarcoma."
Documents the convergent RTK/RAS/PIK3CA genomic axis in rhabdomyosarcoma, of which RAS-MAPK and PI3K-AKT are the downstream effector arms.
Immune-Evasive Tumor Microenvironment
Fusion-positive rhabdomyosarcoma can develop an immune-cold and fibroblast-supported tumor microenvironment, with reduced T-cell infiltration, impaired antigen presentation, immune-checkpoint expression, cancer-associated fibroblast cytokine support, and resistance to chemotherapy or immunotherapy.
Immune-Evasive and Fibroblast-Supported TME Model
cancer-associated fibroblast CL:0000057 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves cancer-associated fibroblast, annotated with fibroblast (CL:0000057). CL:0000057 is a cell type from the Cell Ontology. T cell CL:0000084 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves T cell (CL:0000084). CL:0000084 is a cell type from the Cell Ontology.
antigen processing and presentation GO:0019882 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased antigen processing and presentation (GO:0019882). GO:0019882 is a biological process from the Gene Ontology. ↓ DECREASED immune response GO:0006955 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased immune response (GO:0006955). GO:0006955 is a biological process from the Gene Ontology. ↓ DECREASED
Experimental models
Fusion-positive RMS cancer-associated fibroblast coculture CO CULTURE Tests CAF-mediated growth and treatment-resistance effects.
Downstream
Aberrant Cell Proliferation Cancer-associated fibroblast secreted factors support fusion-positive RMS tumor-cell growth, migration, and treatment resistance. Immune-Evasive and Fibroblast-Supported TME Model
Chemotherapy Resistance and Relapse Cancer-associated fibroblast support can add a microenvironmental treatment-resistance layer on top of tumor-cell-intrinsic resistance circuitry. Immune-Evasive and Fibroblast-Supported TME Model
Metastatic Disease Fibroblast-supported migration is a plausible contributor to metastatic progression in fusion-positive RMS. The edge is deliberately indirect: the cited coculture study measures migration, while the clinical source establishes metastasis as a frequent outcome of the fusion-positive alveolar subtype. Immune-Evasive and Fibroblast-Supported TME Model
Show evidence (2 references)
PMID:41007114 SUPPORT Other
"Additionally, the presence of fusion oncogenes, such as PAX3:FOXO1, hampers immunogenicity and treatment response by disrupting antigen presentation and reducing immune cell infiltration."
Supports a fusion-oncogene-linked immune-evasion mechanism, although the review is broader pediatric RMS rather than ARMS-only.
PMID:41131073 SUPPORT In Vitro
"The cancer-associated fibroblasts also promoted expression of immune checkpoints and conferred resistance to cyclophosphamide, a chemotherapy commonly used to treat this disease."
Directly supports a fibroblast-mediated microenvironmental resistance layer in fusion-positive rhabdomyosarcoma.
Blocked Myogenic Differentiation
Fusion-driven transcriptional and enhancer reprogramming impairs the normal terminal myogenic differentiation program. Tumor cells retain skeletal muscle lineage markers but remain trapped in a malignant, incompletely differentiated state.
cell differentiation GO:0030154 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cell differentiation (GO:0030154). GO:0030154 is a biological process from the Gene Ontology. ↓ DECREASED
Experimental models
Patient-derived ARMS single-cell culture model PRIMARY CELL CULTURE Tests whether tumor-cell states can be redirected toward myogenic differentiation.
Show evidence (1 reference)
PMID:40508013 SUPPORT Other
"We discuss the central role of fusion proteins in transcriptional reprogramming, impaired myogenic differentiation, and super-enhancer activation."
Directly supports impaired myogenic differentiation as an output of the fusion-driven transcriptional/enhancer program.
Aberrant Cell Proliferation
Malignant growth is the convergent output of multiple now-explicit upstream mechanisms: PAX-FOXO1 enhancer reprogramming, ETS1/KDM3A chromatin cofactor dependence, YOD1/N-Myc feedback and protein stabilization, FGFR/RAS/PI3K signaling, and treatment-resistant relapse states.
CDK4 hgnc:1773 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves CDK4 (hgnc:1773). hgnc:1773 is a gene from the HUGO Gene Nomenclature Committee.
cell population proliferation GO:0008283 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased cell population proliferation (GO:0008283). GO:0008283 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Soft Tissue Neoplasm Sustained malignant proliferation produces the soft-tissue tumor mass that defines rhabdomyosarcoma clinically. This is a disease-level output, not a claim about a particular primary anatomic site.
Show evidence (1 reference)
PMID:41401084 SUPPORT Model Organism
"Knocking down YOD1 or inhibiting it with G5 could suppress FP-RMS growth both in vitro and in vivo, through promoting the degradation of both PAX-FOXO1 and N-Myc."
Supports YOD1/N-Myc feedback as a concrete upstream mechanism sustaining proliferative growth.
✶

Histopathology

1
Alveolar or solid-sheet rhabdomyosarcoma morphology
Contemporary histologic classification requires predominantly alveolar architecture or solid sheets of primitive monotonous round cells. Histology and FOXO1-fusion status are complementary: histologic ARMS can be fusion-negative, while rare non-alveolar tumors can carry a PAX-FOXO1 fusion.
Show evidence (1 reference)
PMID:28058850 SUPPORT Other
"The current histologic definition of ARMS requires that the majority of a tumor show alveolar histology, or solid sheets of cells with monotonous round nuclei characteristic of ARMS."
Directly supports the defining contemporary histologic pattern rather than only the generic classification of RMS as a mesenchymal malignancy.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Alveolar Rhabdomyosarcoma Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

5
Eye 1
Proptosis HP:0000520 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Proptosis (HP:0000520). HP:0000520 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39792629 SUPPORT Human Clinical
"Patients in both groups presented with eyelid edema followed by proptosis with similar symptom duration (p = 0.31)."
Supports proptosis in orbital RMS; no ARMS-specific frequency is inferred from this mixed-histology cohort.
Neoplasm 1
Soft Tissue Neoplasm HP:0031459 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Soft tissue neoplasm (HP:0031459). HP:0031459 is a phenotype from the Human Phenotype Ontology.
Sequelae: Proptosis Regional Nodal Disease Intracranial Extension
Show evidence (1 reference)
PMID:40508013 SUPPORT Other
"Alveolar rhabdomyosarcoma (ARMS) is a highly aggressive pediatric soft-tissue sarcoma driven by PAX3/7-FOXO1 fusion proteins."
Supports the soft-tissue neoplasm phenotype without asserting an unevidenced presentation frequency or site distribution.
Other 3
Metastatic Disease
Show evidence (2 references)
PMID:41131073 SUPPORT Other
"The PAX3/PAX7-FOXO1 fusion-positive alveolar subtype has poor clinical outcomes, with frequent recurrence, metastasis, and low survival."
Supports recurrence and metastasis specifically in fusion-positive ARMS without extrapolating a mixed-RMS cohort percentage to this disorder.
PMID:32044412 SUPPORT Human Clinical
"All 7 patients with distant metastases as the first site of recurrence had central nervous system metastases."
Adds direct human-cohort evidence for distant metastatic recurrence in pediatric parameningeal ARMS without extrapolating a page-wide frequency.
Regional Nodal Disease
Show evidence (1 reference)
PMID:32044412 SUPPORT Human Clinical
"N1 disease and intracranial extension (ICE) portended inferior overall survival (P = .002 and .02, respectively)."
Directly supports regional node-positive disease as an adverse feature in a pediatric parameningeal ARMS cohort.
Intracranial Extension
Show evidence (1 reference)
PMID:32044412 SUPPORT Human Clinical
"Most patients had group III (96%), node-negative (67%), positive FOX fusion status (63%) disease, and intracranial extension (54%)."
Directly quantifies intracranial extension in the defined pediatric parameningeal ARMS cohort.
🧬

Genetic Associations

4
PAX3-FOXO1 Fusion (Somatic Fusion Oncogene)
Gene: PAX3 hgnc:8617 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is PAX3 (hgnc:8617). hgnc:8617 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (1 reference)
PMID:39686893 SUPPORT Human Clinical
"According to literature data, the frequency of the PAX3::FOXO1 translocation is 70-90% and the PAX7::FOXO1 translocation 10-30%."
Supports PAX3-FOXO1 as the dominant fusion-positive subtype in alveolar rhabdomyosarcoma.
PAX7-FOXO1 Fusion (Somatic Fusion Oncogene)
Gene: PAX7 hgnc:8621 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is PAX7 (hgnc:8621). hgnc:8621 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (2 references)
PMID:39686893 SUPPORT Human Clinical
"According to literature data, the frequency of the PAX3::FOXO1 translocation is 70-90% and the PAX7::FOXO1 translocation 10-30%."
Supports PAX7-FOXO1 as a recurrent minority fusion-positive subtype in alveolar rhabdomyosarcoma.
PMID:22454413 SUPPORT Human Clinical
"Among nonmetastatic patients, patients who were PAX3/FOXO1 positive had a significantly poorer outcome compared with both alveolar-negative and PAX7/FOXO1-positive patients."
Supports the relative prognostic statement for the PAX7-FOXO1 fusion.
MYCN Amplification (Secondary Genetic Event)
Gene: MYCN hgnc:7559 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is MYCN (hgnc:7559). hgnc:7559 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (1 reference)
PMID:24436047 SUPPORT Human Clinical
"Amplification of 2p24 involving MYCN (5%) occurred predominantly in PFP tumors (8 PFP vs. 1 PFN)"
Documents recurrent MYCN amplification occurring predominantly in fusion-positive (PFP) rhabdomyosarcoma as a cooperating genetic event.
CDK4 Amplification (Secondary Genetic Event)
Gene: CDK4 hgnc:1773 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is CDK4 (hgnc:1773). hgnc:1773 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (1 reference)
PMID:41828638 SUPPORT Other
"amplification of the 12q13-q14 chromosomal region involves a gene-rich region in which there are at least two critical protein-coding oncogenic targets (CDK4 and SHMT2)."
Directly supports CDK4 as an oncogenic target of the recurrent 12q13-q14 amplification in ARMS.
💊

Medical Actions

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Multi-Agent Chemotherapy
Action: Combination ChemotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Combination Chemotherapy (NCIT:C191). NCIT:C191 is a clinical intervention from the NCI Thesaurus. NCIT:C191 Regimen: VAC regimenNCI Thesaurus (NCIT) Relation: this regimen component is this clinical intervention This regimen component is VAC regimen (NCIT:C67299). NCIT:C67299 is a clinical intervention from the NCI Thesaurus. Ontology label: VAC Regimen NCIT:C67299
Agent: vincristine CHEBI:28445 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses vincristine (CHEBI:28445). CHEBI:28445 is a therapeutic agent from Chemical Entities of Biological Interest. actinomycin D CHEBI:27666 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses actinomycin D (CHEBI:27666). CHEBI:27666 is a therapeutic agent from Chemical Entities of Biological Interest. cyclophosphamide CHEBI:4026 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses cyclophosphamide, annotated with cyclophosphamide hydrate (CHEBI:4026). CHEBI:4026 is a therapeutic agent from Chemical Entities of Biological Interest.
Intensive chemotherapy with vincristine, actinomycin D, and cyclophosphamide (VAC) forms the North American backbone of treatment.
Show evidence (1 reference)
PMID:41038289 SUPPORT Other
"Although the gene fusions PAX3::FOXO1 and PAX7::FOXO1 were discovered in the early 1990s, and since that time shown to be the molecular drivers of the disease, the best treatment to date still remains VAC (vincristine, actinomycin D, cyclophosphamide) combination therapy, first instituted as..."
Directly supports the named VAC backbone in fusion-positive RMS rather than only the nonspecific statement that therapy is intensive.
European IVA Induction Chemotherapy
Action: Combination ChemotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Combination Chemotherapy (NCIT:C191). NCIT:C191 is a clinical intervention from the NCI Thesaurus. NCIT:C191
Agent: ifosfamide CHEBI:5864 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses ifosfamide (CHEBI:5864). CHEBI:5864 is a therapeutic agent from Chemical Entities of Biological Interest. vincristine CHEBI:28445 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses vincristine (CHEBI:28445). CHEBI:28445 is a therapeutic agent from Chemical Entities of Biological Interest. actinomycin D CHEBI:27666 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses actinomycin D (CHEBI:27666). CHEBI:27666 is a therapeutic agent from Chemical Entities of Biological Interest.
Ifosfamide, vincristine, and actinomycin D (IVA) is the European induction backbone for high-risk localized RMS. Evidence is RMS-wide and includes ARMS; it does not establish superiority over VAC.
Show evidence (1 reference)
PMID:41038289 SUPPORT Other
"IVA remains the standard induction regimen for high-risk localized RMS in Europe"
Directly supports the European IVA induction backbone while preserving the review-level evidence classification.
Vinorelbine and Low-Dose Cyclophosphamide Maintenance
Action: Combination ChemotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Combination Chemotherapy (NCIT:C191). NCIT:C191 is a clinical intervention from the NCI Thesaurus. NCIT:C191
Agent: vinorelbine CHEBI:480999 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses vinorelbine (CHEBI:480999). CHEBI:480999 is a therapeutic agent from Chemical Entities of Biological Interest. cyclophosphamide CHEBI:4027 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses cyclophosphamide (CHEBI:4027). CHEBI:4027 is a therapeutic agent from Chemical Entities of Biological Interest.
Six cycles of intravenous vinorelbine plus continuous daily low-dose oral cyclophosphamide after remission-producing standard treatment improved overall survival in the EpSSG RMS 2005 randomized phase III trial. Eligible high-risk groups included nonmetastatic ARMS; this is a European standard and not an ARMS-only trial result.
Show evidence (2 references)
PMID:31562043 SUPPORT Human Clinical
"those with non-metastatic alveolar rhabdomyosarcoma but without nodal involvement. Patients in remission after standard treatment"
Directly documents inclusion of nonmetastatic ARMS in the phase III maintenance trial.
PMID:31562043 SUPPORT Human Clinical
"5-year overall survival was 86·5% (95% CI 80·2-90·9) with maintenance chemotherapy versus 73·7% (65·8-80·1) without"
Directly supports the randomized overall-survival benefit; the disease-free-survival endpoint did not cross its significance threshold.
Cixutumumab or Temozolomide Intensification
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
COG ARST08P1 evaluated adding either cixutumumab or temozolomide to an intensive metastatic-RMS chemotherapy backbone. Both nonrandomized pilot regimens were feasible but neither improved outcome; they are retained as negative clinical evidence and are not presented as standards of care.
Show evidence (1 reference)
PMID:30351457 REFUTE Human Clinical
"Neither agent improved outcome compared with the same chemotherapy that was used on ARST0431."
Directly refutes clinical benefit from either intensification strategy in the metastatic RMS pilot cohorts, most of which had alveolar histology.
Surgical Resection
Action: Definitive Surgical ResectionNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Definitive Surgical Resection (NCIT:C154430). NCIT:C154430 is a clinical intervention from the NCI Thesaurus. NCIT:C154430
Complete surgical resection with negative margins when feasible without excessive morbidity. Surgery may be delayed until after chemotherapy to facilitate resection.
Show evidence (1 reference)
PMID:39809723 SUPPORT Human Clinical
"Advances in local control therapy of RMS have improved outcomes after surgical resection of the primary tumor, either before or after induction chemotherapy, even in the setting of metastatic disease."
Supports surgical resection as an established local-control modality in rhabdomyosarcoma, including after induction chemotherapy.
Radiation Therapy
Action: Radiation TherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Radiation Therapy (NCIT:C15313). NCIT:C15313 is a clinical intervention from the NCI Thesaurus. NCIT:C15313
Radiation therapy is used for local control, particularly when complete surgical resection is not possible or margins are positive.
Show evidence (1 reference)
PMID:32124549 SUPPORT Human Clinical
"Patients with FOXO1 positivity who received RT had superior EFS compared with those who did not (77.8% vs 16.7%; P = 0.03)."
Supports adjuvant radiation therapy in FOXO1-positive alveolar rhabdomyosarcoma, even after complete resection.
PAX-FOXO1/ETS1 Complex Disruption
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: YK-4-279 CHEBI:94301 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses YK-4-279 (CHEBI:94301). CHEBI:94301 is a therapeutic agent from Chemical Entities of Biological Interest.
Investigational small-molecule disruption of the PAX3-FOXO1/ETS1 complex is a direct chromatin-handle strategy: it aims to displace PAX3-FOXO1 from disease enhancers and suppress fusion-dependent gene regulation rather than treating the fusion as an untargetable upstream abstraction.
Mechanism Target:
INHIBITS ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module — Disrupts the ETS1-dependent PAX3-FOXO1 chromatin complex and thereby reduces fusion occupancy and target-gene regulation.
Show evidence (1 reference)
PMID:39448867 SUPPORT In Vitro
"YK-4-279 displaces PAX3-FOXO1 from chromatin and interferes with PAX3-FOXO1-dependent gene regulation, resulting in potent inhibition of growth and invasive properties in FP-RMS, along with downregulation of FGF8, IL4R, MEST and PODXL expression."
Shows that the compound acts at the modeled ETS1/PAX3-FOXO1 chromatin cofactor node and suppresses downstream malignant behavior.
Show evidence (1 reference)
PMID:39448867 SUPPORT In Vitro
"We further show that the PAX3-FOXO1/ETS1 complex can be disrupted by the clinically relevant small molecule inhibitor YK-4-279."
Supports YK-4-279-like disruption of the PAX3-FOXO1/ETS1 complex as an investigational therapeutic mechanism.
YOD1 Inhibition
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Investigational YOD1 inhibition is modeled as a feedback-loop intervention: inhibiting YOD1 destabilizes both PAX-FOXO1 and N-Myc, reducing the reciprocal oncogenic amplification loop rather than targeting only a downstream proliferation phenotype.
Mechanism Target:
INHIBITS YOD1-N-Myc PAX-FOXO1 Feedback Loop — Inhibits YOD1-mediated stabilization of PAX-FOXO1 and N-Myc, collapsing the positive feedback loop.
Show evidence (1 reference)
PMID:41401084 SUPPORT Model Organism
"Knocking down YOD1 or inhibiting it with G5 could suppress FP-RMS growth both in vitro and in vivo, through promoting the degradation of both PAX-FOXO1 and N-Myc."
Directly supports the treatment-mechanism link between YOD1 inhibition and disruption of the modeled feedback loop.
Show evidence (1 reference)
PMID:41401084 SUPPORT Model Organism
"Knocking down YOD1 or inhibiting it with G5 could suppress FP-RMS growth both in vitro and in vivo, through promoting the degradation of both PAX-FOXO1 and N-Myc."
Supports YOD1 inhibition as a preclinical strategy that destabilizes both oncogenic proteins and suppresses FP-RMS growth.
FGFR Inhibitor Therapy
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: FGF401 (roblitinib) NCIT:C120102 NCI Thesaurus (NCIT) Relation: this treatment uses this therapeutic agent This treatment uses FGF401 (roblitinib), annotated with Roblitinib (NCIT:C120102). NCIT:C120102 is a therapeutic agent from the NCI Thesaurus. lenvatinib CHEBI:85994 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses lenvatinib (CHEBI:85994). CHEBI:85994 is a therapeutic agent from Chemical Entities of Biological Interest.
Investigational FGFR-directed therapy may be relevant in fusion-positive ARMS with high FGFR4/FGF8 signaling activity. Preclinical models and early translational evidence support FGFR4-selective and multikinase FGFR inhibition as precision-therapy approaches in this molecular subset.
Mechanism Target:
INHIBITS FGFR-Driven RTK Signaling — FGFR4-selective and multikinase FGFR inhibitors block the upstream receptor tyrosine kinase node, not the downstream RAS/PI3K effector arm; RAS- or PIK3CA-level alterations therefore predict potential resistance.
Show evidence (1 reference)
PMID:42041178 SUPPORT Model Organism
"We demonstrate marked tumor growth inhibition in all FP-RMS PDXs treated with single-agent FGF401 (FGFR4-specific inhibitor) and single-agent lenvatinib (multikinase FGFR inhibitor)"
FGFR-directed agents act at the FGFR4 receptor tyrosine kinase node, the upstream step now represented separately from the RAS/PI3K arm.
Show evidence (2 references)
PMID:42041178 SUPPORT Model Organism
"We demonstrate marked tumor growth inhibition in all FP-RMS PDXs treated with single-agent FGF401 (FGFR4-specific inhibitor) and single-agent lenvatinib (multikinase FGFR inhibitor)"
Supports preclinical FGFR-directed efficacy in fusion-positive RMS patient-derived xenograft models.
PMID:42041178 SUPPORT Human Clinical
"report a clinical response to lenvatinib in a patient with relapsed metastatic FP-RMS."
Supports an early human clinical response signal for FGFR-directed therapy in relapsed metastatic fusion-positive RMS.
Histone Deacetylase Inhibitor Therapy
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: entinostat CHEBI:132082 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses entinostat (CHEBI:132082). CHEBI:132082 is a therapeutic agent from Chemical Entities of Biological Interest.
Investigational class I histone deacetylase inhibition, exemplified by entinostat in PAX3::FOXO1-positive ARMS PDX models, targets the HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 chemotherapy-resistance circuit and may resensitize relapsed or resistant disease to RMS chemotherapy.
Mechanism Target:
INHIBITS HDAC3-SMARCA4-miR-27a Chemotherapy Resistance Circuit — HDAC inhibition is modeled as acting on the HDAC3-SMARCA4-miR-27a checkpoint-adaptation circuit that mediates chemotherapy resistance.
Show evidence (1 reference)
PMID:39147820 SUPPORT Model Organism
"Chemotherapy resistance in ARMS has previously been attributed to PAX3::FOXO1-mediated cell cycle checkpoint adaptation, which is mediated by an HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit that can be disrupted by HDAC3 inhibition."
Directly links HDAC3 inhibition to disruption of the modeled chemotherapy-resistance circuit.
Show evidence (1 reference)
PMID:39147820 SUPPORT Model Organism
"We identified single agent, additive or synergistic relationships between relapse-specific chemotherapies and clinically relevant drug exposures of entinostat in three PAX3::FOXO1+ ARMS mouse models."
Supports entinostat as a preclinical combination strategy in PAX3::FOXO1-positive ARMS models.
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Biochemical Markers

4
PAX-FOXO1 Fusion Detection
Show evidence (1 reference)
PMID:39686893 SUPPORT Human Clinical
"Thirty-two tumor samples were collected and analyzed using a combination of histological, immunohistochemistry (Myogenin, MyoD1), and molecular genetic techniques (fluorescence in situ hybridization (FISH) and real-time polymerase chain reaction (RT-PCR))."
Directly supports use of FISH and RT-PCR for routine PAX-FOXO1 fusion detection in clinical ARMS pathology.
Myogenic Markers
Show evidence (1 reference)
PMID:39686893 SUPPORT Human Clinical
"Thirty-two tumor samples were collected and analyzed using a combination of histological, immunohistochemistry (Myogenin, MyoD1), and molecular genetic techniques"
Directly supports use of myogenin and MyoD1 immunohistochemistry as standard diagnostic markers in ARMS.
Baseline circulating tumor DNA
Show evidence (2 references)
DOI:10.1200/jco.22.00409 SUPPORT Human Clinical
"Identification of pathognomonic translocations between PAX3 or PAX7 and FOXO1 by Rhabdo-Seq was the best method for measuring ctDNA in FP-RMS and detected ctDNA in 27 of 49 cases (55%)."
Directly supports fusion-junction ctDNA detection in a clinical FP-RMS cohort.
DOI:10.1200/jco.22.00409 SUPPORT Human Clinical
"as did patients with FP-RMS (event-free survival, 37% v 70%; P = .045; overall survival, 39.2% v 75%; P = .023)."
Supports prognostic association in fusion-positive RMS while not claiming independent significance in the smaller FP-RMS subgroup.
Elevated serum lactate dehydrogenase
Show evidence (1 reference)
PMID:40790568 SUPPORT Human Clinical
"elevated serum lactate dehydrogenase at diagnosis above 400 U/L (HR = 2.80; 95% CI 1.46-5.33; p = 0.002)"
Directly supports elevated baseline LDH as an adverse prognostic finding in the mixed-histology pediatric RMS cohort.
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Diagnosis

2
Histologic and immunohistochemical classification
Tissue diagnosis evaluates the contemporary alveolar or solid-sheet morphology and myogenic differentiation markers. Morphology establishes the histologic class, while myogenin and MyoD1 support rhabdomyoblastic differentiation.
immunohistochemistry NCIT:C23020 NCI Thesaurus (NCIT)
Markers: Myogenin; MyoD1
Results: Alveolar architecture or solid sheets of monotonous round cells with myogenic-marker expression
Show evidence (2 references)
PMID:28058850 SUPPORT Other
"The current histologic definition of ARMS requires that the majority of a tumor show alveolar histology, or solid sheets of cells with monotonous round nuclei characteristic of ARMS."
Defines the contemporary histologic classification criterion.
PMID:39686893 SUPPORT Human Clinical
"Thirty-two tumor samples were collected and analyzed using a combination of histological, immunohistochemistry (Myogenin, MyoD1), and molecular genetic techniques"
Supports the combined morphology, myogenic-marker, and molecular workflow in a clinical ARMS series.
PAX3/7-FOXO1 fusion testing
FISH, RT-PCR, or sequencing is used to establish FOXO1 rearrangement and identify the fusion partner. Fusion status refines prognosis and treatment stratification but does not replace the histologic classification.
genetic testing NCIT:C15709 NCI Thesaurus (NCIT)
Markers: PAX3-FOXO1; PAX7-FOXO1; FOXO1 rearrangement
Results: Fusion-positive, fusion-negative, or alternative PAX fusion
Show evidence (2 references)
PMID:28058850 SUPPORT Other
"The PAX3-FOXO1 and PAX7-FOXO1 gene fusions occur in 80% of cases with the alveolar subtype and are more predictive of outcome than histologic classification."
Supports routine ascertainment of fusion status for molecular and prognostic classification.
PMID:39686893 SUPPORT Human Clinical
"Cytogenetic analysis using the FISH technique with a FOXO1-specific probe identified 26 (81%) samples with rearrangements at the FOXO1 locus and seven (19%) without rearrangements."
Directly supports FOXO1 FISH testing in a clinical ARMS cohort.
📈

Progression

2
Early treatment failure in parameningeal ARMS
In a small single-institution cohort treated with chemotherapy and proton radiotherapy, failures occurred early and included local recurrence and central-nervous-system metastasis. These site-specific estimates should not be generalized to all ARMS.
Show evidence (1 reference)
PMID:32044412 SUPPORT Human Clinical
"The 3-year local control, regional control, disease-free survival, and overall survival rates were 66%, 94%, 40%, and 58%, respectively. Median time to any failure was 0.5 years (range, 0.2-2.1)."
Directly quantifies timing and outcomes in a defined pediatric parameningeal ARMS cohort.
Progression or relapse after upfront metastatic RMS
Pooled cooperative-group data show that progression or relapse after metastatic RMS carries very poor survival. This cohort spans RMS histologies and is used to describe the metastatic disease state, not an ARMS-only rate.
Show evidence (1 reference)
PMID:41721480 SUPPORT Human Clinical
"3-year Overall Survival for FEC from first event was 8.0% (95% CI 6.1-10.2)."
Directly supports the poor post-progression or post-relapse prognosis in the pooled metastatic RMS cohort.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Alveolar Rhabdomyosarcoma:

Embryonal rhabdomyosarcoma MONDO:0009993
Overlapping Features ERMS shares skeletal-muscle differentiation and can overlap clinically with ARMS. Fusion-negative tumors called ARMS by morphology frequently resemble ERMS molecularly and clinically, so morphology and fusion status must be reported separately.
Distinguishing Features
  • Predominantly alveolar architecture or monotonous solid-sheet cytology supports ARMS histology.
  • A PAX3-FOXO1 or PAX7-FOXO1 fusion supports fusion-positive RMS biology and adverse-risk stratification.
  • Fusion-negative alveolar histology has molecular and clinical behavior closer to ERMS.
Show evidence (2 references)
PMID:28058850 SUPPORT Other
"Further, gene expression profiling of RMS shows ARMSn is highly similar to ERMS"
Supports the important molecular overlap between fusion-negative alveolar-histology RMS and ERMS.
PMID:28058850 SUPPORT Other
"Historically, pediatric RMS has been classified into two groups; alveolar RMS (ARMS) composed of primitive monotonous round cells typically with scant cytoplasm, and embryonal RMS (ERMS) with a range of appearances from small moderately pleomorphic cells to spindle cells that can have abundant..."
Directly states the principal histologic distinction.
B-lymphoblastic lymphoma Not Yet Curated MONDO:0000873
Overlapping Features An orbital lymphoblastic lymphoma can mimic the clinical and radiologic presentation of orbital rhabdomyosarcoma. Tissue histopathology and lineage-directed immunophenotyping distinguish the entities. The evidence is a single pediatric case and establishes a diagnostic pitfall rather than its frequency in an ARMS population.
Distinguishing Features
  • Lymphoid-lineage immunophenotyping supports B-lymphoblastic lymphoma.
  • Myogenin and MyoD1 expression with appropriate morphology supports rhabdomyosarcoma.
  • FOXO1 rearrangement testing further resolves fusion-positive RMS biology.
Show evidence (1 reference)
PMID:41986061 SUPPORT Human Clinical
"Due to overlapping clinical and radiological features, these cases are often misdiagnosed initially, with rhabdomyosarcoma being a common provisional diagnosis."
Directly supports orbital B-lymphoblastic lymphoma as a clinical and radiologic mimic requiring tissue lineage confirmation.
📊

Related Datasets

5
Histone H3K27ac ChIP-seq, PAX3-FOXO1 ChIP-seq, BRD4 ChIP-seq, DNase-seq, RNA-seq and 4C-seq in FP-RMS cell lines and patient-derived cultures (Gryder et al. 2017 Cancer Discovery SuperSeries) geo:GSE83728
Foundational epigenomic atlas of the PAX3-FOXO1 super-enhancer regulatory program in fusion-positive ARMS. Includes H3K27ac, BRD4, MED1, MYOD, MYOG, MYCN, CTCF, and PAX3-FOXO1 ChIP-seq across RH3, RH4, RH5, RH41 (FP-ARMS), RD (ERMS), and patient-derived primary cultures (≥10 donors), plus a causal fibroblast model (7250 cells ± PAX3-FOXO1). DNase-seq and 4C-seq provide chromatin-accessibility and 3D contact data. Subseries GSE83726 contains H3K27ac ChIP-seq from primary human ARMS tumor biopsies. Defines the BET-bromodomain vulnerability of the PAX3-FOXO1 transcriptional program.
human MULTI OMICS n=80 Illumina HiSeq 2000/2500
alveolar rhabdomyosarcoma cell line UBERON:0001134 Uberon multi-species anatomy ontology (UBERON) Relation: this dataset samples this sample type This dataset samples alveolar rhabdomyosarcoma cell line, annotated with skeletal muscle tissue (UBERON:0001134). UBERON:0001134 is a sample type from the Uberon multi-species anatomy ontology.
Conditions: fusion-positive alveolar rhabdomyosarcoma (FP-ARMS) embryonal rhabdomyosarcoma (FN-RMS) normal fibroblast ± PAX3-FOXO1
PMID:28446439
SuperSeries; subseries GSE83724 (RNA-seq), GSE83725 (fibroblast causal model ChIP/DNase), GSE83726 (primary tumor H3K27ac), GSE83727 (4C-seq). The fibroblast subseries (GSE83725) provides the cleanest causal model for PAX3-FOXO1 pioneer-factor chromatin remodelling independent of pre-existing RMS epigenome.
Show evidence (1 reference)
PMID:28446439 SUPPORT In Vitro
"We find PAX3-FOXO1 reprograms the cis-regulatory landscape by inducing de novo super enhancers."
The dataset's companion study defines the PAX3-FOXO1 super-enhancer program that this epigenomic atlas maps.
dTAG-mediated PAX3-FOXO1 degradation time-course in FP-RMS: ATAC-seq, PRO-seq, ChIP-seq, CUT&RUN, RNA-seq (Gryder et al. 2022) geo:GSE183281
Most causally informative ARMS dataset available. Uses dTAG-mediated targeted degradation of endogenously tagged PAX3-FOXO1 in RH4 and RH30 cell lines with time-resolved multi-omics (0.5–72 h). ATAC-seq tracks chromatin accessibility loss in real time; PRO-seq captures nascent enhancer RNA transcription to identify active super-enhancer elements; CUT&RUN maps histone marks; RNA-seq defines direct vs. indirect gene expression responses. SuperSeries comprising 10 subseries (≥209 samples total). Definitively distinguishes immediate-early PAX3-FOXO1 direct targets from secondary transcriptional cascades.
human MULTI OMICS PERTURBATION n=209 Illumina NovaSeq 6000
alveolar rhabdomyosarcoma cell line UBERON:0001134 Uberon multi-species anatomy ontology (UBERON) Relation: this dataset samples this sample type This dataset samples alveolar rhabdomyosarcoma cell line, annotated with skeletal muscle tissue (UBERON:0001134). UBERON:0001134 is a sample type from the Uberon multi-species anatomy ontology.
Conditions: PAX3-FOXO1 dTAG degradation (0.5–72 h time course) DMSO control
PMID:36395771
SuperSeries (GSE183281); 10 component subseries covering ATAC-seq, PRO-seq, ChIP-seq, CUT&RUN, and RNA-seq in RH4 and RH30 lines. The PRO-seq component is unique — capturing eRNA transcription at active super-enhancers provides the most direct readout of PAX3-FOXO1 SE activity available in any published ARMS dataset.
Show evidence (1 reference)
PMID:36395771 SUPPORT In Vitro
"We used a chemical-genetic approach to rapidly degrade a canonical transcriptional activator, PAX3-FOXO1, to define the mechanism by which it regulates gene expression programs."
Describes the rapid PAX3-FOXO1 degradation strategy that generated this time-resolved multi-omics dataset.
Single-cell transcriptomics of alveolar rhabdomyosarcoma identifies PAX3::FOXO1-maintained progenitor state (Danielli et al. 2023) geo:GSE218974
scRNA-seq of patient-derived aRMS and eRMS primary cultures plus RH4/RH30 cell lines (~53,000 cells total). Identifies a PAX3::FOXO1-stabilized "myogenin+ cycling progenitor" cell state that persists across individual tumors. PAX3::FOXO1 shRNA knockdown releases the differentiation block and shifts cells toward a myogenin-high differentiated state. Companion CyTOF mass cytometry and a 244-compound phenotypic drug screen (MYOscopy imaging) identify MEK inhibitor (trametinib) + RAF inhibitor (dabrafenib) as cell- fate hijackers that redirect aRMS toward differentiation. Survival analysis shows the progenitor/MuSC-like transcriptional signature correlates with inferior patient outcomes.
human SINGLE CELL RNA SEQ n=7 10x Genomics Chromium; Illumina NovaSeq 6000
alveolar rhabdomyosarcoma cell UBERON:0001134 Uberon multi-species anatomy ontology (UBERON) Relation: this dataset samples this sample type This dataset samples alveolar rhabdomyosarcoma cell, annotated with skeletal muscle tissue (UBERON:0001134). UBERON:0001134 is a sample type from the Uberon multi-species anatomy ontology.
Conditions: alveolar rhabdomyosarcoma (aRMS) patient-derived cultures embryonal rhabdomyosarcoma (eRMS) PAX3::FOXO1 shRNA knockdown
PMID:36753540
GEO series GSE218974 (7 samples, ~53,000 cells). Companion CyTOF data and 244-compound drug screen (MYOscopy) data are not deposited to GEO but are described in PMID:36753540. Most ARMS-focused scRNA-seq dataset; directly interrogates the PAX3::FOXO1 cell-fate lock with perturbation experiments.
Show evidence (1 reference)
PMID:36753540 SUPPORT In Vitro
"Here, we combined single-cell RNA sequencing, mass cytometry, and high-content imaging to resolve intratumoral heterogeneity of patient-derived primary RMS cultures."
Supports the patient-derived single-cell culture dataset and its multimodal profiling design.
Single-cell and single-nucleus RNA-seq + scATAC-seq atlas of pediatric rhabdomyosarcoma with lineage tracking and therapy-resistant states (Patel et al. 2022 Dev Cell) geo:GSE174376
Comprehensive single-cell atlas (122,731 nuclei/cells) from 18 primary patient tumors (6 ARMS + 12 ERMS), 18 orthotopic PDX models, and organoids. Multi-modal: snRNA-seq (frozen tumors), scRNA-seq (fresh), scATAC-seq (paired chromatin accessibility), and lentiviral barcode lineage tracking. Defines a 3-state myogenic developmental hierarchy (progenitor / myoblast-like / myocyte-like) shared across subtypes. ARMS shows a narrower late-stage developmental bias vs. ERMS. scATAC-seq links chromatin accessibility to cell-state transitions. Chemotherapy selects for ABCG2+ mesoderm-like quiescent progenitor cells, providing a mechanistic model for disease relapse. Includes matched pre/post-treatment samples from RMS13 clinical trial.
human SINGLE CELL RNA SEQ n=64 10x Genomics Chromium; Illumina...
rhabdomyosarcoma tumor UBERON:0001134 Uberon multi-species anatomy ontology (UBERON) Relation: this dataset samples this sample type This dataset samples rhabdomyosarcoma tumor, annotated with skeletal muscle tissue (UBERON:0001134). UBERON:0001134 is a sample type from the Uberon multi-species anatomy ontology.
Conditions: alveolar rhabdomyosarcoma (ARMS) embryonal rhabdomyosarcoma (ERMS) treatment-naive post-chemotherapy
PMID:35483358
GEO series GSE174376. Uniformly processed open-access downloads available via ScPCA project SCPCP000005 (Alex's Lemonade Stand Foundation) as SingleCellExperiment and AnnData objects. The paired scATAC-seq (6 samples) is the only publicly available chromatin-accessibility data from primary human ARMS patient tissue.
Show evidence (1 reference)
PMID:35483358 SUPPORT In Vitro
"Here, we use single-cell and single-nucleus RNA sequencing to show that RMS tumors recapitulate the spectrum of embryonal myogenesis."
Supports the principal single-cell and single-nucleus dataset design; ARMS-specific sample composition is accession metadata rather than a claim established by this abstract sentence.
Comprehensive genomic analysis of rhabdomyosarcoma — WGS, WES, and RNA-seq of primary human tumors (Shern et al. 2014 Cancer Discovery) dbgap:phs000720
Reference multi-platform genomic landscape study of primary human rhabdomyosarcoma. Includes WGS (44 tumor/normal pairs at ~105× depth), WES (103 tumor/normal pairs), RNA-seq (80 tumors), and SNP arrays (865 consented subjects in dbGaP v5). PAX3-FOXO1 (n≈35) and PAX7-FOXO1 (n≈15) fusion-positive cases dominate the cohort. Establishes that the RTK/RAS/PIK3CA genetic axis is altered in 93% of cases, revealing a framework for genomics-directed therapy. Identifies the recurrent secondary somatic landscape (MYCN amplification, CDK4/CDKN2A alterations, TP53 mutations) co-occurring with PAX fusions. Publicly accessible mutation summary and expression data via cBioPortal study rms_nih_2014; raw BAM/VCF files require dbGaP controlled-access approval.
human MULTI OMICS n=147 Illumina HiSeq 2000; Illumina Omni...
rhabdomyosarcoma tumor UBERON:0001134 Uberon multi-species anatomy ontology (UBERON) Relation: this dataset samples this sample type This dataset samples rhabdomyosarcoma tumor, annotated with skeletal muscle tissue (UBERON:0001134). UBERON:0001134 is a sample type from the Uberon multi-species anatomy ontology.
Conditions: fusion-positive rhabdomyosarcoma (PAX3-FOXO1 and PAX7-FOXO1) fusion-negative rhabdomyosarcoma
PMID:24436047
dbGaP accession phs000720 (currently v5.p2). Open summary-level mutation and expression data accessible via cBioPortal study rms_nih_2014 (https://www.cbioportal.org/study/summary?id=rms_nih_2014). This is the same study cited in the genetic and pathophysiology sections (PMID:24436047); the dataset entry enables direct linkage to the raw data repository.
Show evidence (1 reference)
PMID:24436047 SUPPORT Human Clinical
"Here, we report a collaborative effort between the National Cancer Institute, the Children's Oncology Group, and the Broad Institute using a combination of whole-genome, whole-exome and whole-transcriptome sequencing along with high resolution SNP arrays to characterize the landscape of somatic..."
Directly supports the multi-platform design, collaborators, and cohort size represented by this dbGaP record.
🔬

Clinical Trials

1
NCT02567435 PHASE_III ACTIVE_NOT_RECRUITING
Children's Oncology Group ARST1431 compares VAC alternating with vincristine/irinotecan against the same chemotherapy plus temsirolimus in intermediate-risk RMS. Alveolar rhabdomyosarcoma is an eligible condition; the registry is not an ARMS-only efficacy study.
Show evidence (1 reference)
clinicaltrials:NCT02567435 SUPPORT Human Clinical
"This randomized phase III trial studies how well combination chemotherapy (vincristine sulfate, dactinomycin, cyclophosphamide alternated with vincristine sulfate and irinotecan hydrochloride or vinorelbine) works compared to combination chemotherapy plus temsirolimus in treating patients with..."
The ClinicalTrials.gov record directly documents the phase III intermediate-risk RMS comparison; it is not interpreted as proof of benefit before results are available.
🧫

Experimental Models

2
Patient-derived ARMS single-cell culture model PRIMARY_CELL_CULTURE
Patient-derived aRMS cultures resolve cycling progenitor, muscle stem-like, and differentiated states and enable perturbational testing of RAF/MEK inhibitors. Culture-state findings require confirmation in clinical tumors.
skeletal muscle myoblast CL:0000515 Cell Ontology (CL) Relation: this experimental model uses this cell type This experimental model uses skeletal muscle myoblast (CL:0000515). CL:0000515 is a cell type from the Cell Ontology.
Organism
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Tissue
skeletal muscle tissue UBERON:0001134 Uberon multi-species anatomy ontology (UBERON) Relation: this experimental model uses this anatomical location This experimental model uses skeletal muscle tissue (UBERON:0001134). UBERON:0001134 is an anatomical location from the Uberon multi-species anatomy ontology.
Cell source
Patient-derived primary RMS cultures
Culture
Primary tumor culture profiled by single-cell RNA sequencing, mass cytometry, and high-content imaging
Publication
PMID:36753540
Pathograph links
Blocked Myogenic Differentiation Tests whether tumor-cell states can be redirected toward myogenic differentiation.
Show evidence (1 reference)
PMID:36753540 SUPPORT In Vitro
"We screened for drugs hijacking aRMS toward clinically favorable subpopulations and identified a combination of RAF and MEK inhibitors that potently induces myogenic differentiation and inhibits tumor growth."
Directly links the culture model to the differentiation mechanism and perturbation.
Show evidence (1 reference)
PMID:36753540 SUPPORT In Vitro
"Here, we combined single-cell RNA sequencing, mass cytometry, and high-content imaging to resolve intratumoral heterogeneity of patient-derived primary RMS cultures."
Directly establishes the experimental system and assay suite.
Fusion-positive RMS cancer-associated fibroblast coculture CO_CULTURE
A human coculture model tests fibroblast-secreted support of FP-RMS growth, migration, immune-checkpoint expression, and cyclophosphamide resistance. It represents one metastatic microenvironment and does not establish the prevalence of this state across patients.
cancer-associated fibroblast CL:0000057 Cell Ontology (CL) Relation: this experimental model uses this cell type This experimental model uses cancer-associated fibroblast, annotated with fibroblast (CL:0000057). CL:0000057 is a cell type from the Cell Ontology. skeletal muscle myoblast CL:0000515 Cell Ontology (CL) Relation: this experimental model uses this cell type This experimental model uses skeletal muscle myoblast (CL:0000515). CL:0000515 is a cell type from the Cell Ontology.
Organism
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Cell source
Metastatic fusion-positive RMS-derived fibroblasts and fusion-positive RMS tumor cells
Culture
Tumor-cell and fibroblast conditioned-medium/coculture model
Publication
PMID:41131073
Pathograph links
Immune-Evasive Tumor Microenvironment Tests CAF-mediated growth and treatment-resistance effects.
Show evidence (1 reference)
PMID:41131073 SUPPORT In Vitro
"The cancer-associated fibroblasts also promoted expression of immune checkpoints and conferred resistance to cyclophosphamide, a chemotherapy commonly used to treat this disease."
Directly supports the immune-checkpoint and resistance outputs of the coculture model.
Show evidence (1 reference)
PMID:41131073 SUPPORT In Vitro
"This study establishes a model of cancer-associated fibroblasts from metastatic fusion-positive rhabdomyosarcoma."
Directly establishes the disease-specific fibroblast model.
🐁

Animal Models

2
Patient-derived xenografts of PAX3-FOXO1 fusion-positive rhabdomyosarcoma Mus musculus Patient-derived xenograft
Fusion-positive RMS PDXs preserve patient-tumor context for testing the FGFR4-selective inhibitor roblitinib and multikinase inhibitor lenvatinib. They support preclinical response, not population-level clinical efficacy.
Species
Mus musculus
Genotype
Patient-derived xenografts of PAX3-FOXO1 fusion-positive rhabdomyosarcoma
Show evidence (1 reference)
PMID:42041178 SUPPORT Model Organism
"We demonstrate marked tumor growth inhibition in all FP-RMS PDXs treated with single-agent FGF401 (FGFR4-specific inhibitor) and single-agent lenvatinib (multikinase FGFR inhibitor)"
Directly establishes the FP-RMS PDX treatment model and its preclinical response endpoint.
PAX3::FOXO1-positive alveolar rhabdomyosarcoma mouse and PDX models Mus musculus Genetically engineered and patient-derived tumor models
Three PAX3::FOXO1-positive ARMS mouse models were used to test entinostat at clinically relevant exposure alone and with relapse-directed chemotherapy. Model-specific synergy does not establish human efficacy.
Species
Mus musculus
Genotype
PAX3::FOXO1-positive alveolar rhabdomyosarcoma mouse and PDX models
Show evidence (1 reference)
PMID:39147820 SUPPORT Model Organism
"We identified single agent, additive or synergistic relationships between relapse-specific chemotherapies and clinically relevant drug exposures of entinostat in three PAX3::FOXO1+ ARMS mouse models."
Directly defines the number, genotype, intervention, and use of the models.
{ }

Source YAML

click to show 
name: Alveolar Rhabdomyosarcoma
creation_date: '2026-01-26T02:55:13Z'
description: >-
  Alveolar rhabdomyosarcoma (ARMS) is an aggressive pediatric soft tissue sarcoma
  characterized by skeletal muscle differentiation and distinctive chromosomal
  translocations involving PAX3 or PAX7 fused to FOXO1. Among fusion-positive
  tumors, PAX3-FOXO1 arising from t(2;13)(q35;q14) is the dominant fusion
  subtype, reported in roughly 70-90% of cases, and confers a worse prognosis.
  PAX7-FOXO1 from t(1;13)(p36;q14) accounts for most of the remaining
  fusion-positive cases and is generally associated with somewhat better
  outcomes. Approximately 20% are fusion-negative and behave more like
  embryonal rhabdomyosarcoma. The PAX-FOXO1 fusion proteins function as
  aberrant transcription factors driving myogenic differentiation arrest and
  proliferation.
categories:
- Pediatric Cancer
- Soft Tissue Sarcoma
- Sarcoma
parents:
- rhabdomyosarcoma
has_subtypes:
- name: PAX3-FOXO1 Fusion-Positive
  description: >-
    The most common and aggressive subtype, harboring the t(2;13)(q35;q14)
    translocation. Associated with older age at diagnosis, extremity primary
    sites, and inferior survival compared to other subtypes.
  evidence:
  - reference: PMID:39686893
    reference_title: "[Characteristics of the cytogenetic variants of alveolar rhabdomyosarcoma]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "According to literature data, the frequency of the PAX3::FOXO1 translocation is 70-90% and the PAX7::FOXO1 translocation 10-30%."
    explanation: Supports PAX3-FOXO1 as the dominant fusion-positive subtype in alveolar rhabdomyosarcoma.
  - reference: PMID:22454413
    reference_title: PAX3/FOXO1 fusion gene status is the key prognostic molecular marker in rhabdomyosarcoma and significantly improves current risk stratification.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Among nonmetastatic patients, patients who were PAX3/FOXO1 positive had a
      significantly poorer outcome compared with both alveolar-negative and
      PAX7/FOXO1-positive patients.
    explanation: >-
      Directly supports the poorer prognosis asserted for the PAX3-FOXO1
      subtype relative to the other molecular groups.
- name: PAX7-FOXO1 Fusion-Positive
  description: >-
    Harbors the t(1;13)(p36;q14) translocation. This is the less common
    FOXO1-rearranged subtype and is generally associated with better prognosis
    than PAX3-FOXO1 positive tumors.
  evidence:
  - reference: PMID:39686893
    reference_title: "[Characteristics of the cytogenetic variants of alveolar rhabdomyosarcoma]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "According to literature data, the frequency of the PAX3::FOXO1 translocation is 70-90% and the PAX7::FOXO1 translocation 10-30%."
    explanation: Supports PAX7-FOXO1 as a recurrent minority fusion-positive subtype in alveolar rhabdomyosarcoma.
  - reference: PMID:22454413
    reference_title: PAX3/FOXO1 fusion gene status is the key prognostic molecular marker in rhabdomyosarcoma and significantly improves current risk stratification.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Among nonmetastatic patients, patients who were PAX3/FOXO1 positive had a
      significantly poorer outcome compared with both alveolar-negative and
      PAX7/FOXO1-positive patients.
    explanation: >-
      Supports the relative outcome distinction between PAX7-FOXO1-positive and
      PAX3-FOXO1-positive nonmetastatic disease.
- name: Fusion-Negative Alveolar Rhabdomyosarcoma
  description: >-
    Approximately 20% of histologically defined ARMS lack PAX-FOXO1 fusions.
    These tumors have clinical behavior and molecular features more similar
    to embryonal rhabdomyosarcoma.
  evidence:
  - reference: PMID:39686893
    reference_title: "[Characteristics of the cytogenetic variants of alveolar rhabdomyosarcoma]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Approximately 20% of cases of alveolar RMS do not have cytogenetic signs of rearrangements of the FOXO1 gene."
    explanation: Directly supports the existence of fusion-negative ARMS at approximately 20% frequency.
progression:
- phase: Early treatment failure in parameningeal ARMS
  notes: >-
    In a small single-institution cohort treated with chemotherapy and proton
    radiotherapy, failures occurred early and included local recurrence and
    central-nervous-system metastasis. These site-specific estimates should not
    be generalized to all ARMS.
  evidence:
  - reference: PMID:32044412
    reference_title: Patterns of Failure in Parameningeal Alveolar Rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The 3-year local control, regional control, disease-free survival, and
      overall survival rates were 66%, 94%, 40%, and 58%, respectively. Median
      time to any failure was 0.5 years (range, 0.2-2.1).
    explanation: >-
      Directly quantifies timing and outcomes in a defined pediatric
      parameningeal ARMS cohort.
- phase: Progression or relapse after upfront metastatic RMS
  notes: >-
    Pooled cooperative-group data show that progression or relapse after
    metastatic RMS carries very poor survival. This cohort spans RMS histologies
    and is used to describe the metastatic disease state, not an ARMS-only rate.
  evidence:
  - reference: PMID:41721480
    reference_title: "Children and Young People With First Relapse or Progression of Upfront Metastatic Rhabdomyosarcoma: An Analysis of Clinical Features and Outcomes From the INternational Soft Tissue saRcoma ConsorTium (INSTRuCT)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      3-year Overall Survival for FEC from first event was 8.0% (95% CI
      6.1-10.2).
    explanation: >-
      Directly supports the poor post-progression or post-relapse prognosis in
      the pooled metastatic RMS cohort.
mechanistic_hypotheses:
- hypothesis_group_id: canonical_fusion_regulatory_program
  hypothesis_label: Canonical PAX-FOXO1 Fusion Regulatory Program
  status: CANONICAL
  description: >-
    PAX3/7-FOXO1 is the initiating molecular driver of fusion-positive ARMS and
    produces a fusion-dependent transcriptional and enhancer state that blocks
    myogenic differentiation and supports malignant behavior.
  notes: >-
    This hypothesis group is intentionally not a fully ordered linear chain.
    Edges from the fusion regulatory program to sibling outputs should be read
    as curated disease-model links supported at the current graph granularity,
    not as proof that all sibling outputs are causally upstream of one another.
  evidence:
  - reference: PMID:40508013
    reference_title: "Molecular Targets in Alveolar Rhabdomyosarcoma: A Narrative Review of Progress and Pitfalls."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "We discuss the central role of fusion proteins in transcriptional reprogramming, impaired myogenic differentiation, and super-enhancer activation."
    explanation: >-
      Supports the canonical fusion-to-regulatory-program model used to group
      the core pathograph edges.
- hypothesis_group_id: chromatin_feedback_maintenance_model
  hypothesis_label: Chromatin-Cofactor and Protein-Stability Feedback Model
  status: EMERGING
  description: >-
    ETS1/KDM3A chromatin cofactor activity and YOD1/N-Myc protein-stability
    feedback are candidate maintenance mechanisms for the PAX3-FOXO1 regulatory
    state. They are not modeled as downstream consequences of measured open
    chromatin; they are candidate inputs or feedback arms that can be tested
    against a chromatin-state readout.
  notes: >-
    Current evidence supports biochemical interaction, chromatin occupancy,
    target-gene regulation, and growth effects. It does not yet fully resolve
    whether these mechanisms are required upstream of all disease-defining
    chromatin features, restricted to a subset of target loci, or partly
    downstream adaptive programs.
  evidence:
  - reference: PMID:39448867
    reference_title: Dependence of PAX3-FOXO1 chromatin occupancy on ETS1 at important disease-promoting genes exposes new targetable vulnerability in Fusion-Positive Rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We show that ETS1, which is induced by both PAX3-FOXO1 and KDM3A, exists
      in complex with PAX3-FOXO1, and augments PAX3-FOXO1 chromatin occupancy.
    explanation: >-
      Supports ETS1/KDM3A as a candidate chromatin-maintenance arm of the
      fusion-dependent regulatory model.
  - reference: PMID:41401084
    reference_title: Therapeutic targeting of YOD1 disrupts the PAX-FOXO1/N-Myc feedback loop in rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The reciprocal transcriptional activation of PAX3-FOXO1 and N-Myc is
      critical for FP-RMS malignancy.
    explanation: >-
      Supports the YOD1/N-Myc branch as a feedback-maintenance hypothesis rather
      than a simple downstream proliferation marker.
- hypothesis_group_id: fgfr_downstream_output_dependency_model
  hypothesis_label: FGFR/FGF8 Downstream Output Dependency Model
  status: EMERGING
  description: >-
    A subset of fusion-positive RMS shows high FGF8/FGFR4 expression, FGFR4
    phosphorylation, and FGFR inhibitor response. This is modeled as a
    downstream output or branch dependency unless perturbation evidence shows
    that FGFR signaling feeds back to maintain the fusion chromatin state.
  notes: >-
    This grouping separates a druggable output branch from the core chromatin
    regulatory-state hypothesis. FGF8 enhancer occupancy supports a link to the
    fusion/cofactor program, while FGFR4 phosphorylation and inhibitor response
    support branch activity and therapeutic relevance.
  evidence:
  - reference: PMID:42041178
    reference_title: Comprehensive Multiplatform Tyrosine Kinase Profiling Reveals Novel Actionable FGFR Aberrations across Sarcomas Affecting the Young.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We highlight the utility of FGFR inhibitors in PAX3-FOXO1
      fusion-positive rhabdomyosarcomas (FP-RMS) characterized by high FGFR4
      and FGF8 RNA expression levels and FGFR4 activation (FGFR4_pY).
    explanation: >-
      Supports a distinct FGFR4/FGF8 output branch in fusion-positive RMS.
- hypothesis_group_id: therapy_resistance_branch_model
  hypothesis_label: HDAC3 Chemotherapy-Resistance Branch Model
  status: EMERGING
  description: >-
    PAX3::FOXO1-mediated checkpoint adaptation and the
    HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit form a therapy-context resistance
    branch that contributes to relapse under chemotherapy pressure.
  notes: >-
    This group should not be conflated with the initiating ARMS regulatory
    program. It is a curated resistance branch that may affect chromatin state
    in resistant disease, but the cited evidence primarily supports
    chemotherapy-resistance biology.
  evidence:
  - reference: PMID:39147820
    reference_title: Entinostat as a combinatorial therapeutic for rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Chemotherapy resistance in ARMS has previously been attributed to
      PAX3::FOXO1-mediated cell cycle checkpoint adaptation, which is mediated
      by an HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit that can be disrupted by
      HDAC3 inhibition.
    explanation: >-
      Supports the HDAC3 circuit as a chemotherapy-resistance branch linked to
      PAX3::FOXO1 biology.
- hypothesis_group_id: microenvironment_support_model
  hypothesis_label: Immune-Evasive and Fibroblast-Supported TME Model
  status: EMERGING
  description: >-
    Fusion-positive RMS can acquire an immune-cold and fibroblast-supported
    tumor microenvironment that promotes growth, migration, immune evasion, and
    chemotherapy resistance.
  notes: >-
    The evidence is strongest for fibroblast-supported growth and
    cyclophosphamide resistance in fusion-positive RMS models. The edge from
    fusion state to immune evasion remains broader and partially supported.
  evidence:
  - reference: PMID:41131073
    reference_title: Cancer-associated fibroblasts promote tumor progression in fusion-positive rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Compared to normal lung fibroblasts, these cancer-associated fibroblasts
      secreted distinct factors that specifically supported the growth and
      migration of fusion-positive rhabdomyosarcoma cells.
    explanation: >-
      Supports the fibroblast-supported microenvironment model in
      fusion-positive RMS.
pathophysiology:
- name: PAX-FOXO1 Fusion Oncogene
  description: >-
    The t(2;13) or t(1;13) translocations fuse the DNA-binding domain of PAX3
    or PAX7 with the transactivation domain of FOXO1. The resulting fusion
    protein functions as a potent aberrant transcription factor that activates
    PAX target genes to supraphysiological levels, driving proliferation while
    blocking terminal myogenic differentiation.
  evidence:
  - reference: PMID:39686893
    reference_title: "[Characteristics of the cytogenetic variants of alveolar rhabdomyosarcoma]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "According to literature data, the frequency of the PAX3::FOXO1 translocation is 70-90% and the PAX7::FOXO1 translocation 10-30%."
    explanation: "Supports the prevalence of PAX3/7-FOXO1 fusions in alveolar rhabdomyosarcoma."
  - reference: PMID:24436047
    reference_title: Comprehensive genomic analysis of rhabdomyosarcoma reveals a landscape of alterations affecting a common genetic axis in fusion-positive and fusion-negative tumors.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      As expected, the defining genomic alteration seen across the entire
      cohort was recurrent t(2;13) or t(1;13), that resulted in a fusion of the
      N-terminus of PAX3 or PAX7 to the C-terminus of FOXO1
    explanation: >-
      Directly supports the translocation structure and resulting PAX-FOXO1
      fusion in human RMS tumors.
  cell_types:
  - preferred_term: skeletal muscle myoblast
    term:
      id: CL:0000515
      label: skeletal muscle myoblast
  genes:
  - preferred_term: PAX3
    term:
      id: hgnc:8617
      label: PAX3
  - preferred_term: PAX7
    term:
      id: hgnc:8621
      label: PAX7
  - preferred_term: FOXO1
    term:
      id: hgnc:3819
      label: FOXO1
  biological_processes:
  - preferred_term: positive regulation of transcription by RNA polymerase II
    modifier: ABNORMAL
    term:
      id: GO:0045944
      label: positive regulation of transcription by RNA polymerase II
  locations:
  - preferred_term: skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  downstream:
  - target: PAX-FOXO1 Disease Enhancer Reprogramming
    description: >-
      The fusion oncogene establishes an aberrant enhancer and super-enhancer
      transcriptional program that sits between the chromosomal fusion and
      phenotype-level outputs.
    causal_link_type: DIRECT
    hypothesis_groups:
    - canonical_fusion_regulatory_program
    evidence:
    - reference: PMID:40508013
      reference_title: "Molecular Targets in Alveolar Rhabdomyosarcoma: A Narrative Review of Progress and Pitfalls."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "We discuss the central role of fusion proteins in transcriptional reprogramming, impaired myogenic differentiation, and super-enhancer activation."
      explanation: >-
        Supports enhancer and super-enhancer reprogramming as the mechanistic
        layer downstream of the fusion oncoprotein.
- name: PAX-FOXO1 Disease Enhancer Reprogramming
  description: >-
    PAX-FOXO1 does not act as a generic "oncogene" in the pathograph; it
    rewires chromatin occupancy, enhancer activity, and transcriptional output.
    This node is the inferred regulatory program, not the ATAC-seq/open
    chromatin measurement itself. Disease-specific open chromatin is an
    assayable projection of this program and can be used to test whether
    perturbing candidate maintenance machinery changes the regulatory state
    itself, as opposed to changing downstream or branch-specific outputs such
    as FGFR signaling, immune evasion, or chemotherapy resistance.
  evidence:
  - reference: PMID:40508013
    reference_title: "Molecular Targets in Alveolar Rhabdomyosarcoma: A Narrative Review of Progress and Pitfalls."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "We discuss the central role of fusion proteins in transcriptional reprogramming, impaired myogenic differentiation, and super-enhancer activation."
    explanation: >-
      Establishes transcriptional reprogramming and super-enhancer activation
      as central mechanisms in ARMS.
  cell_types:
  - preferred_term: skeletal muscle myoblast
    term:
      id: CL:0000515
      label: skeletal muscle myoblast
  biological_processes:
  - preferred_term: chromatin remodeling
    modifier: ABNORMAL
    term:
      id: GO:0006338
      label: chromatin remodeling
  - preferred_term: positive regulation of gene expression
    modifier: ABNORMAL
    term:
      id: GO:0010628
      label: positive regulation of gene expression
  downstream:
  - target: ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module
    description: >-
      The fusion regulatory program induces ETS1 and intersects with KDM3A;
      this edge marks the entry into a feedback/cofactor module, not a claim
      that measured open chromatin causes the cofactor state.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - PAX3-FOXO1-dependent ETS1 induction
    - KDM3A-dependent ETS1 induction
    hypothesis_groups:
    - chromatin_feedback_maintenance_model
    evidence:
    - reference: PMID:39448867
      reference_title: Dependence of PAX3-FOXO1 chromatin occupancy on ETS1 at important disease-promoting genes exposes new targetable vulnerability in Fusion-Positive Rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        We show that ETS1, which is induced by both PAX3-FOXO1 and KDM3A, exists
        in complex with PAX3-FOXO1, and augments PAX3-FOXO1 chromatin occupancy.
      explanation: >-
        Supports PAX3-FOXO1/KDM3A induction of ETS1 and the resulting
        cofactor relationship, while the exact ordering of enhancer-state
        change versus cofactor maintenance remains incompletely resolved.
  - target: YOD1-N-Myc PAX-FOXO1 Feedback Loop
    description: >-
      Fusion-driven transcription induces an N-Myc feedback state in which
      N-Myc also activates PAX-FOXO1 expression and complexes with the fusion
      protein.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - N-Myc induction downstream of PAX-FOXO1
    - reciprocal PAX3-FOXO1/N-Myc transcriptional activation
    hypothesis_groups:
    - chromatin_feedback_maintenance_model
    evidence:
    - reference: PMID:41401084
      reference_title: Therapeutic targeting of YOD1 disrupts the PAX-FOXO1/N-Myc feedback loop in rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Here, we discovered that N-Myc, in addition to being a classic
        downstream target of PAX-FOXO1, can also activate its expression and
        form a transcriptional complex with PAX-FOXO1, thereby markedly
        amplifying oncogenic signaling.
      explanation: >-
        Supports a reciprocal PAX-FOXO1/N-Myc transcriptional feedback layer
        rather than a one-way downstream target model.
  - target: HDAC3-SMARCA4-miR-27a Chemotherapy Resistance Circuit
    description: >-
      PAX3::FOXO1-mediated cell-cycle checkpoint adaptation creates a
      treatment-resistance branch mediated by the
      HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - PAX3::FOXO1-mediated cell-cycle checkpoint adaptation
    - HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit
    hypothesis_groups:
    - therapy_resistance_branch_model
    evidence:
    - reference: PMID:39147820
      reference_title: Entinostat as a combinatorial therapeutic for rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Chemotherapy resistance in ARMS has previously been attributed to
        PAX3::FOXO1-mediated cell cycle checkpoint adaptation, which is mediated
        by an HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit that can be disrupted by
        HDAC3 inhibition.
      explanation: >-
        Supports the missing causal edge from the fusion-driven transcriptional
        program to the HDAC3-linked chemotherapy-resistance circuit.
  - target: Blocked Myogenic Differentiation
    description: >-
      Fusion-driven enhancer reprogramming impairs the terminal skeletal muscle
      differentiation program.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - fusion-dependent transcriptional reprogramming
    - suppression of terminal myogenic differentiation programs
    hypothesis_groups:
    - canonical_fusion_regulatory_program
    evidence:
    - reference: PMID:40508013
      reference_title: "Molecular Targets in Alveolar Rhabdomyosarcoma: A Narrative Review of Progress and Pitfalls."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "We discuss the central role of fusion proteins in transcriptional reprogramming, impaired myogenic differentiation, and super-enhancer activation."
      explanation: >-
        Supports the differentiation blockade as a direct output of the fusion
        transcriptional/enhancer program.
  - target: Immune-Evasive Tumor Microenvironment
    description: >-
      Fusion oncogene activity contributes to reduced antigen presentation and
      immune-cell infiltration, creating an immune-evasive tumor state.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - altered antigen presentation
    - reduced immune-cell infiltration
    - specific fusion-regulated immune-evasion targets remain incompletely resolved
    hypothesis_groups:
    - microenvironment_support_model
    evidence:
    - reference: PMID:41007114
      reference_title: "Tumor-Immune Interactions in Pediatric Oral Rhabdomyosarcoma: A Narrative Review on Immuno-Oncology and Emerging Therapies."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Additionally, the presence of fusion oncogenes, such as PAX3:FOXO1,
        hampers immunogenicity and treatment response by disrupting antigen
        presentation and reducing immune cell infiltration.
      explanation: >-
        Supports a fusion-linked route to immune evasion, though the review is
        broader pediatric RMS rather than ARMS-only.
- name: ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module
  description: >-
    KDM3A and ETS1 form a disease-promoting chromatin cofactor axis with
    PAX3-FOXO1. ETS1 is induced by PAX3-FOXO1 and KDM3A, complexes with
    PAX3-FOXO1, augments fusion occupancy at enhancers, and helps maintain
    disease-promoting target genes including FGF8, IL4R, MEST, and PODXL. This
    is a direct mechanistic handle because YK-4-279 disrupts the
    PAX3-FOXO1/ETS1 complex and displaces PAX3-FOXO1 from chromatin.
  evidence:
  - reference: PMID:39448867
    reference_title: Dependence of PAX3-FOXO1 chromatin occupancy on ETS1 at important disease-promoting genes exposes new targetable vulnerability in Fusion-Positive Rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We show that ETS1, which is induced by both PAX3-FOXO1 and KDM3A, exists
      in complex with PAX3-FOXO1, and augments PAX3-FOXO1 chromatin occupancy.
    explanation: >-
      Directly supports ETS1 as a PAX3-FOXO1 chromatin cofactor in
      fusion-positive RMS.
  biological_processes:
  - preferred_term: chromatin remodeling
    modifier: ABNORMAL
    term:
      id: GO:0006338
      label: chromatin remodeling
  - preferred_term: positive regulation of gene expression
    modifier: ABNORMAL
    term:
      id: GO:0010628
      label: positive regulation of gene expression
  downstream:
  - target: PAX-FOXO1 Disease Enhancer Reprogramming
    description: >-
      ETS1/KDM3A cofactor activity is modeled as a candidate maintenance input
      into the fusion-dependent enhancer program, not as a downstream
      consequence of the ATAC-seq accessibility measurement.
    causal_link_type: DIRECT
    hypothesis_groups:
    - chromatin_feedback_maintenance_model
    evidence:
    - reference: PMID:39448867
      reference_title: Dependence of PAX3-FOXO1 chromatin occupancy on ETS1 at important disease-promoting genes exposes new targetable vulnerability in Fusion-Positive Rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        We show that ETS1, which is induced by both PAX3-FOXO1 and KDM3A, exists
        in complex with PAX3-FOXO1, and augments PAX3-FOXO1 chromatin occupancy.
      explanation: >-
        Supports the cofactor module as a candidate causal input into
        fusion-protein chromatin occupancy.
  - target: FGFR-Driven RTK Signaling
    description: >-
      The cofactor module occupies and regulates disease-promoting enhancers
      including FGF8, which links the fusion/cofactor chromatin program to the
      FGF8/FGFR4 output branch. This does not by itself prove that FGFR signaling
      maintains the upstream chromatin state.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - PAX3-FOXO1/ETS1/KDM3A occupancy at the FGF8 enhancer
    - FGF8 expression in the FGFR4/FGF8 branch
    - FGFR4 phosphorylation in responsive fusion-positive RMS models
    hypothesis_groups:
    - chromatin_feedback_maintenance_model
    - fgfr_downstream_output_dependency_model
    evidence:
    - reference: PMID:39448867
      reference_title: Dependence of PAX3-FOXO1 chromatin occupancy on ETS1 at important disease-promoting genes exposes new targetable vulnerability in Fusion-Positive Rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        KDM3A and ETS1 colocalize with PAX3-FOXO1 to enhancers of important
        disease-promoting genes in FP-RMS, including FGF8, IL4R, and MEST, as
        well as PODXL, which we define herein as a new FP-RMS-promoting gene.
      explanation: >-
        Places FGF8 under the PAX3-FOXO1/ETS1/KDM3A enhancer module, supporting
        the ligand-side bridge to the FGFR branch but not direct FGFR activation
        by the cofactor module.
    - reference: PMID:42041178
      reference_title: Comprehensive Multiplatform Tyrosine Kinase Profiling Reveals Novel Actionable FGFR Aberrations across Sarcomas Affecting the Young.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        We highlight the utility of FGFR inhibitors in PAX3-FOXO1
        fusion-positive rhabdomyosarcomas (FP-RMS) characterized by high FGFR4
        and FGF8 RNA expression levels and FGFR4 activation (FGFR4_pY).
      explanation: >-
        Supports the downstream FGFR4/FGF8 branch that the FGF8 enhancer link
        is proposed to feed.
  - target: Aberrant Cell Proliferation
    description: >-
      Disrupting the PAX3-FOXO1/ETS1 complex inhibits growth and invasive
      properties, implying that this cofactor module sustains malignant tumor
      cell behavior.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - PAX3-FOXO1/ETS1 complex disruption
    - reduced PAX3-FOXO1 chromatin occupancy
    - altered FGF8, IL4R, MEST, and PODXL expression
    hypothesis_groups:
    - chromatin_feedback_maintenance_model
    evidence:
    - reference: PMID:39448867
      reference_title: Dependence of PAX3-FOXO1 chromatin occupancy on ETS1 at important disease-promoting genes exposes new targetable vulnerability in Fusion-Positive Rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        YK-4-279 displaces PAX3-FOXO1 from chromatin and interferes with
        PAX3-FOXO1-dependent gene regulation, resulting in potent inhibition of
        growth and invasive properties in FP-RMS, along with downregulation of
        FGF8, IL4R, MEST and PODXL expression.
      explanation: >-
        Functional inhibition of the cofactor complex suppresses FP-RMS growth
        and invasion in vitro.
- name: YOD1-N-Myc PAX-FOXO1 Feedback Loop
  description: >-
    N-Myc is both a downstream target and a reciprocal activator of
    PAX-FOXO1. YOD1 stabilizes both PAX-FOXO1 and N-Myc, maintaining a positive
    feedback loop that amplifies oncogenic signaling. This creates a second
    targetable handle upstream of generic proliferation: destabilize the two
    oncogenic proteins together rather than treating N-Myc as only a downstream
    proliferation marker.
  evidence:
  - reference: PMID:41401084
    reference_title: Therapeutic targeting of YOD1 disrupts the PAX-FOXO1/N-Myc feedback loop in rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We further identified YOD1 as a deubiquitinating enzyme that stabilizes
      both PAX-FOXO1 and N-Myc.
    explanation: >-
      Identifies YOD1 as the stabilizing enzyme for both members of the
      PAX-FOXO1/N-Myc feedback loop.
  genes:
  - preferred_term: MYCN
    term:
      id: hgnc:7559
      label: MYCN
  biological_processes:
  - preferred_term: protein stabilization
    modifier: INCREASED
    term:
      id: GO:0050821
      label: protein stabilization
  - preferred_term: positive regulation of gene expression
    modifier: INCREASED
    term:
      id: GO:0010628
      label: positive regulation of gene expression
  downstream:
  - target: PAX-FOXO1 Disease Enhancer Reprogramming
    description: >-
      Stabilizing PAX-FOXO1 and N-Myc is modeled as a feedback input into the
      fusion-dependent regulatory state. The cited work supports reciprocal
      transcriptional activation and malignancy dependence; whether the full
      ARMS open-chromatin signature collapses after YOD1 inhibition remains an
      explicit open test.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - YOD1-dependent PAX-FOXO1 and N-Myc protein stabilization
    - reciprocal PAX3-FOXO1/N-Myc transcriptional activation
    hypothesis_groups:
    - chromatin_feedback_maintenance_model
    evidence:
    - reference: PMID:41401084
      reference_title: Therapeutic targeting of YOD1 disrupts the PAX-FOXO1/N-Myc feedback loop in rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        The reciprocal transcriptional activation of PAX3-FOXO1 and N-Myc is
        critical for FP-RMS malignancy.
      explanation: >-
        Supports feedback into the fusion-driven oncogenic transcriptional
        state; direct open-chromatin-state maintenance remains to be tested.
  - target: Aberrant Cell Proliferation
    description: >-
      YOD1-dependent stabilization of PAX-FOXO1 and N-Myc sustains FP-RMS
      growth.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - degradation of PAX-FOXO1 and N-Myc after YOD1 knockdown or inhibition
    - collapse of PAX3-FOXO1/N-Myc positive feedback
    hypothesis_groups:
    - chromatin_feedback_maintenance_model
    evidence:
    - reference: PMID:41401084
      reference_title: Therapeutic targeting of YOD1 disrupts the PAX-FOXO1/N-Myc feedback loop in rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Knocking down YOD1 or inhibiting it with G5 could suppress FP-RMS
        growth both in vitro and in vivo, through promoting the degradation of
        both PAX-FOXO1 and N-Myc.
      explanation: >-
        Demonstrates functional growth dependence on YOD1-mediated stabilization
        of PAX-FOXO1 and N-Myc.
- name: HDAC3-SMARCA4-miR-27a Chemotherapy Resistance Circuit
  description: >-
    PAX3::FOXO1-mediated cell-cycle checkpoint adaptation creates a relapse and
    chemotherapy-resistance branch mediated by an
    HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit. This is the mechanistic target
    of HDAC3-directed epigenetic therapy with entinostat-like class I HDAC
    inhibition, not merely a generic "HDAC inhibitor" rationale.
  evidence:
  - reference: PMID:39147820
    reference_title: Entinostat as a combinatorial therapeutic for rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Chemotherapy resistance in ARMS has previously been attributed to
      PAX3::FOXO1-mediated cell cycle checkpoint adaptation, which is mediated
      by an HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit that can be disrupted by
      HDAC3 inhibition.
    explanation: >-
      Defines the HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 resistance circuit and its
      therapeutic vulnerability to HDAC3 inhibition.
  biological_processes:
  - preferred_term: regulation of cell cycle
    modifier: ABNORMAL
    term:
      id: GO:0051726
      label: regulation of cell cycle
  - preferred_term: epigenetic regulation of gene expression
    modifier: ABNORMAL
    term:
      id: GO:0040029
      label: epigenetic regulation of gene expression
  downstream:
  - target: Chemotherapy Resistance and Relapse
    description: >-
      The HDAC3-linked checkpoint adaptation circuit permits tumor cells to
      survive cytotoxic treatment pressure and contributes to relapse.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - PAX3::FOXO1-mediated cell-cycle checkpoint adaptation
    - HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 resistance circuit
    - survival under cytotoxic chemotherapy pressure
    hypothesis_groups:
    - therapy_resistance_branch_model
    evidence:
    - reference: PMID:39147820
      reference_title: Entinostat as a combinatorial therapeutic for rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Chemotherapy resistance in ARMS has previously been attributed to
        PAX3::FOXO1-mediated cell cycle checkpoint adaptation, which is mediated
        by an HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit that can be disrupted by
        HDAC3 inhibition.
      explanation: >-
        Directly supports the HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit as a
        mechanism of chemotherapy resistance.
- name: Chemotherapy Resistance and Relapse
  description: >-
    A clinically important disease state in which initially chemotherapy-
    responsive PAX3::FOXO1-positive ARMS survives treatment pressure, relapses,
    and becomes resistant. In this pathograph it is modeled as a downstream
    output of specific mechanisms, especially the HDAC3-SMARCA4-miR-27a
    checkpoint-adaptation circuit and microenvironmental support, rather than
    as an unexplained late clinical outcome.
  evidence:
  - reference: PMID:39147820
    reference_title: Entinostat as a combinatorial therapeutic for rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Metastatic PAX3::FOXO1+ ARMS often responds to chemotherapies initially,
      only to subsequently relapse and become resistant with most patients
      failing to survive beyond 8 years post-diagnosis.
    explanation: >-
      Supports relapse and acquired chemotherapy resistance as a core clinical
      disease state in metastatic PAX3::FOXO1-positive ARMS.
  biological_processes:
  - preferred_term: response to xenobiotic stimulus
    modifier: ABNORMAL
    term:
      id: GO:0009410
      label: response to xenobiotic stimulus
- name: FGFR-Driven RTK Signaling
  description: >-
    One branch of the fusion-positive ARMS program is receptor tyrosine kinase
    signaling centered on FGFR4, driven by high FGFR4 and FGF8 expression and
    FGFR4 phosphoactivation. This is a directly druggable downstream output
    branch, not currently a proven maintainer of the upstream fusion-dependent
    chromatin state.
  evidence:
  - reference: PMID:42041178
    reference_title: Comprehensive Multiplatform Tyrosine Kinase Profiling Reveals Novel Actionable FGFR Aberrations across Sarcomas Affecting the Young.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We highlight the utility of FGFR inhibitors in PAX3-FOXO1
      fusion-positive rhabdomyosarcomas (FP-RMS) characterized by high FGFR4
      and FGF8 RNA expression levels and FGFR4 activation (FGFR4_pY).
    explanation: >-
      Patient and PDX profiling documents FGFR4 activation as a distinct,
      directly actionable receptor tyrosine kinase input in fusion-positive
      rhabdomyosarcoma.
  biological_processes:
  - preferred_term: fibroblast growth factor receptor signaling pathway
    modifier: INCREASED
    term:
      id: GO:0008543
      label: fibroblast growth factor receptor signaling pathway
  downstream:
  - target: RAS/PI3K Effector Pathway Activation
    description: >-
      FGFR4 signaling is curated as an RTK input to downstream RAS-MAPK and
      PI3K-AKT effector arms. The canonical receptor-to-effector mechanism is
      supported, while ARMS-specific dependence remains context-dependent.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - FRS2 phosphorylation
    - GRB2 adaptor recruitment
    hypothesis_groups:
    - fgfr_downstream_output_dependency_model
    evidence:
    - reference: PMID:28058850
      reference_title: Molecular diagnostics in the management of rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Signaling by FGFR4 and other fibroblast growth factor receptors involves
        tyrosine phosphorylation of the receptor carboxyl terminus along with
        other substrates, such as FRS2, recruitment of the GRB2 adaptor, and
        activation of the downstream RAS and phosphoinositide 3-kinase pathways.
      explanation: >-
        Directly supports FGFR4-to-RAS/PI3K signaling at the pathway level in
        rhabdomyosarcoma molecular diagnostics literature.
    - reference: PMID:24436047
      reference_title: Comprehensive genomic analysis of rhabdomyosarcoma reveals a landscape of alterations affecting a common genetic axis in fusion-positive and fusion-negative tumors.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Furthermore, alteration of the receptor tyrosine kinase/RAS/PIK3CA
        axis affects 93% of cases
      explanation: >-
        Supports the RTK/RAS/PIK3CA axis as a recurrent rhabdomyosarcoma
        pathway context, but not FGFR4-specific pathway dependence in every
        tumor.
- name: RAS/PI3K Effector Pathway Activation
  description: >-
    Receptor tyrosine kinase input converges on the downstream RAS-MAPK and
    PI3K-AKT effector pathways. Genomic profiling shows the combined
    RTK/RAS/PIK3CA axis is altered in the large majority of rhabdomyosarcomas;
    this effector branch is therefore a curated downstream signaling state, not
    a claim that RAS/PI3K activation is the only or universal route to ARMS
    proliferation.
  evidence:
  - reference: PMID:24436047
    reference_title: Comprehensive genomic analysis of rhabdomyosarcoma reveals a landscape of alterations affecting a common genetic axis in fusion-positive and fusion-negative tumors.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Furthermore, alteration of the receptor tyrosine kinase/RAS/PIK3CA
      axis affects 93% of cases, providing a framework for genomics-directed
      therapies that might improve outcomes for patients with
      rhabdomyosarcoma.
    explanation: >-
      Documents the convergent RTK/RAS/PIK3CA genomic axis in rhabdomyosarcoma,
      of which RAS-MAPK and PI3K-AKT are the downstream effector arms.
  biological_processes:
  - preferred_term: Ras protein signal transduction
    modifier: INCREASED
    term:
      id: GO:0007265
      label: Ras protein signal transduction
  - preferred_term: PI3K/AKT signal transduction
    modifier: INCREASED
    term:
      id: GO:0043491
      label: phosphatidylinositol 3-kinase/protein kinase B signal transduction
  downstream:
  - target: Aberrant Cell Proliferation
    description: >-
      RAS-MAPK and PI3K-AKT effector pathway activation is modeled as a
      pro-proliferative and survival output of the RTK/RAS/PIK3CA axis. The
      edge preserves pathograph connectivity but remains qualified: the cited
      ARMS/RMS evidence supports recurrent pathway involvement, not a direct or
      universal ARMS-specific causal step.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - MAPK-dependent cell-cycle entry
    - AKT-dependent survival signaling
    hypothesis_groups:
    - fgfr_downstream_output_dependency_model
    evidence:
    - reference: PMID:24436047
      reference_title: Comprehensive genomic analysis of rhabdomyosarcoma reveals a landscape of alterations affecting a common genetic axis in fusion-positive and fusion-negative tumors.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Furthermore, alteration of the receptor tyrosine kinase/RAS/PIK3CA
        axis affects 93% of cases, providing a framework for genomics-directed
        therapies that might improve outcomes for patients with
        rhabdomyosarcoma.
      explanation: >-
        Supports the RTK/RAS/PIK3CA axis as a recurrent rhabdomyosarcoma
        context; the specific RAS/PI3K-to-proliferation edge is retained as an
        indirect, pathway-level inference rather than direct ARMS-specific proof.
- name: Immune-Evasive Tumor Microenvironment
  description: >-
    Fusion-positive rhabdomyosarcoma can develop an immune-cold and
    fibroblast-supported tumor microenvironment, with reduced T-cell
    infiltration, impaired antigen presentation, immune-checkpoint expression,
    cancer-associated fibroblast cytokine support, and resistance to
    chemotherapy or immunotherapy.
  evidence:
  - reference: PMID:41007114
    reference_title: "Tumor-Immune Interactions in Pediatric Oral Rhabdomyosarcoma: A Narrative Review on Immuno-Oncology and Emerging Therapies."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Additionally, the presence of fusion oncogenes, such as PAX3:FOXO1,
      hampers immunogenicity and treatment response by disrupting antigen
      presentation and reducing immune cell infiltration.
    explanation: >-
      Supports a fusion-oncogene-linked immune-evasion mechanism, although the
      review is broader pediatric RMS rather than ARMS-only.
  - reference: PMID:41131073
    reference_title: Cancer-associated fibroblasts promote tumor progression in fusion-positive rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The cancer-associated fibroblasts also promoted expression of immune
      checkpoints and conferred resistance to cyclophosphamide, a chemotherapy
      commonly used to treat this disease.
    explanation: >-
      Directly supports a fibroblast-mediated microenvironmental resistance
      layer in fusion-positive rhabdomyosarcoma.
  cell_types:
  - preferred_term: cancer-associated fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  - preferred_term: T cell
    term:
      id: CL:0000084
      label: T cell
  biological_processes:
  - preferred_term: antigen processing and presentation
    modifier: DECREASED
    term:
      id: GO:0019882
      label: antigen processing and presentation
  - preferred_term: immune response
    modifier: DECREASED
    term:
      id: GO:0006955
      label: immune response
  downstream:
  - target: Aberrant Cell Proliferation
    description: >-
      Cancer-associated fibroblast secreted factors support fusion-positive RMS
      tumor-cell growth, migration, and treatment resistance.
    causal_link_type: DIRECT
    hypothesis_groups:
    - microenvironment_support_model
    evidence:
    - reference: PMID:41131073
      reference_title: Cancer-associated fibroblasts promote tumor progression in fusion-positive rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Compared to normal lung fibroblasts, these cancer-associated fibroblasts
        secreted distinct factors that specifically supported the growth and
        migration of fusion-positive rhabdomyosarcoma cells.
      explanation: >-
        Supports the causal edge from fibroblast-supported microenvironmental
        signaling to growth and migration of fusion-positive RMS cells.
  - target: Chemotherapy Resistance and Relapse
    description: >-
      Cancer-associated fibroblast support can add a microenvironmental
      treatment-resistance layer on top of tumor-cell-intrinsic resistance
      circuitry.
    causal_link_type: DIRECT
    hypothesis_groups:
    - microenvironment_support_model
    evidence:
    - reference: PMID:41131073
      reference_title: Cancer-associated fibroblasts promote tumor progression in fusion-positive rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        The cancer-associated fibroblasts also promoted expression of immune
        checkpoints and conferred resistance to cyclophosphamide, a chemotherapy
        commonly used to treat this disease.
      explanation: >-
        Supports a direct edge from fibroblast-supported TME state to
        chemotherapy resistance.
  - target: Metastatic Disease
    description: >-
      Fibroblast-supported migration is a plausible contributor to metastatic
      progression in fusion-positive RMS. The edge is deliberately indirect:
      the cited coculture study measures migration, while the clinical source
      establishes metastasis as a frequent outcome of the fusion-positive
      alveolar subtype.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - fibroblast-secreted promigratory factors
    - invasion and dissemination
    hypothesis_groups:
    - microenvironment_support_model
    evidence:
    - reference: PMID:41131073
      reference_title: Cancer-associated fibroblasts promote tumor progression in fusion-positive rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Compared to normal lung fibroblasts, these cancer-associated fibroblasts
        secreted distinct factors that specifically supported the growth and
        migration of fusion-positive rhabdomyosarcoma cells.
      explanation: >-
        Supports the promigratory component of the proposed route, but not the
        complete metastatic cascade in vivo.
    - reference: PMID:41131073
      reference_title: Cancer-associated fibroblasts promote tumor progression in fusion-positive rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        The PAX3/PAX7-FOXO1 fusion-positive alveolar subtype has poor clinical
        outcomes, with frequent recurrence, metastasis, and low survival.
      explanation: >-
        Establishes metastasis as a clinical outcome in fusion-positive ARMS;
        it does not prove that fibroblast support is the sole cause.
- name: Blocked Myogenic Differentiation
  description: >-
    Fusion-driven transcriptional and enhancer reprogramming impairs the normal
    terminal myogenic differentiation program. Tumor cells retain skeletal
    muscle lineage markers but remain trapped in a malignant, incompletely
    differentiated state.
  evidence:
  - reference: PMID:40508013
    reference_title: "Molecular Targets in Alveolar Rhabdomyosarcoma: A Narrative Review of Progress and Pitfalls."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "We discuss the central role of fusion proteins in transcriptional reprogramming, impaired myogenic differentiation, and super-enhancer activation."
    explanation: Directly supports impaired myogenic differentiation as an output of the fusion-driven transcriptional/enhancer program.
  biological_processes:
  - preferred_term: cell differentiation
    modifier: DECREASED
    term:
      id: GO:0030154
      label: cell differentiation
- name: Aberrant Cell Proliferation
  description: >-
    Malignant growth is the convergent output of multiple now-explicit upstream
    mechanisms: PAX-FOXO1 enhancer reprogramming, ETS1/KDM3A chromatin cofactor
    dependence, YOD1/N-Myc feedback and protein stabilization, FGFR/RAS/PI3K
    signaling, and treatment-resistant relapse states.
  evidence:
  - reference: PMID:41401084
    reference_title: Therapeutic targeting of YOD1 disrupts the PAX-FOXO1/N-Myc feedback loop in rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Knocking down YOD1 or inhibiting it with G5 could suppress FP-RMS growth
      both in vitro and in vivo, through promoting the degradation of both
      PAX-FOXO1 and N-Myc.
    explanation: >-
      Supports YOD1/N-Myc feedback as a concrete upstream mechanism sustaining
      proliferative growth.
  biological_processes:
  - preferred_term: cell population proliferation
    modifier: INCREASED
    term:
      id: GO:0008283
      label: cell population proliferation
  genes:
  - preferred_term: CDK4
    term:
      id: hgnc:1773
      label: CDK4
  downstream:
  - target: Soft Tissue Neoplasm
    description: >-
      Sustained malignant proliferation produces the soft-tissue tumor mass
      that defines rhabdomyosarcoma clinically. This is a disease-level output,
      not a claim about a particular primary anatomic site.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - clonal tumor-cell expansion
    evidence:
    - reference: PMID:40508013
      reference_title: "Molecular Targets in Alveolar Rhabdomyosarcoma: A Narrative Review of Progress and Pitfalls."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Alveolar rhabdomyosarcoma (ARMS) is a highly aggressive pediatric soft-tissue sarcoma driven by PAX3/7-FOXO1 fusion proteins."
      explanation: >-
        Supports the disease-level link from the fusion-driven malignant
        program to a soft-tissue sarcoma, while the intervening expansion step
        is represented explicitly.
histopathology:
- name: Alveolar or solid-sheet rhabdomyosarcoma morphology
  finding_term:
    preferred_term: Alveolar rhabdomyosarcoma
    term:
      id: NCIT:C3749
      label: Alveolar Rhabdomyosarcoma
  description: >-
    Contemporary histologic classification requires predominantly alveolar
    architecture or solid sheets of primitive monotonous round cells. Histology
    and FOXO1-fusion status are complementary: histologic ARMS can be
    fusion-negative, while rare non-alveolar tumors can carry a PAX-FOXO1
    fusion.
  evidence:
  - reference: PMID:28058850
    reference_title: Molecular diagnostics in the management of rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The current histologic definition of ARMS requires that the majority of a
      tumor show alveolar histology, or solid sheets of cells with monotonous
      round nuclei characteristic of ARMS.
    explanation: >-
      Directly supports the defining contemporary histologic pattern rather
      than only the generic classification of RMS as a mesenchymal malignancy.

phenotypes:
- category: Musculoskeletal
  name: Soft Tissue Neoplasm
  diagnostic: true
  description: >-
    ARMS is a pediatric soft-tissue sarcoma; the local presentation depends on
    the primary anatomic site. A mass should therefore trigger tissue diagnosis
    rather than serve as a subtype-specific finding by itself.
  phenotype_term:
    preferred_term: Soft tissue neoplasm
    term:
      id: HP:0031459
      label: Soft tissue neoplasm
  evidence:
  - reference: PMID:40508013
    reference_title: "Molecular Targets in Alveolar Rhabdomyosarcoma: A Narrative Review of Progress and Pitfalls."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Alveolar rhabdomyosarcoma (ARMS) is a highly aggressive pediatric soft-tissue sarcoma driven by PAX3/7-FOXO1 fusion proteins."
    explanation: >-
      Supports the soft-tissue neoplasm phenotype without asserting an
      unevidenced presentation frequency or site distribution.
  sequelae:
  - target: Proptosis
    description: >-
      When the primary soft-tissue tumor is orbital, local tumor growth and
      mass effect can manifest as proptosis. This link applies to the orbital
      subset and is not an ARMS-wide frequency claim.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - orbital primary tumor growth
    - orbital mass effect
    evidence:
    - reference: PMID:39792629
      reference_title: "Adult and pediatric orbital rhabdomyosarcoma: comparison of characteristics and outcomes."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Patients in both groups presented with eyelid edema followed by proptosis with similar symptom duration (p = 0.31)."
      explanation: >-
        Supports proptosis as a presentation of orbital RMS; the mass-effect
        pathway is a clinically standard inference and the cohort is not
        restricted to ARMS.
  - target: Regional Nodal Disease
    description: >-
      Local ARMS can spread through regional lymphatics. This is an indirect
      clinical edge and does not imply that every primary tumor develops nodal
      disease.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - lymphatic invasion
    - regional lymphatic dissemination
    evidence:
    - reference: PMID:32044412
      reference_title: Patterns of Failure in Parameningeal Alveolar Rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        N1 disease and intracranial extension (ICE) portended inferior overall
        survival (P = .002 and .02, respectively).
      explanation: >-
        Establishes clinically consequential regional nodal disease in a
        pediatric parameningeal ARMS cohort; the lymphatic route is the stated
        intervening clinical mechanism.
  - target: Intracranial Extension
    description: >-
      Parameningeal tumor growth can extend intracranially because of local
      anatomic continuity. This edge is restricted to the parameningeal subset.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - local invasion from a parameningeal primary
    evidence:
    - reference: PMID:32044412
      reference_title: Patterns of Failure in Parameningeal Alveolar Rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Most patients had group III (96%), node-negative (67%), positive FOX
        fusion status (63%) disease, and intracranial extension (54%).
      explanation: >-
        Directly documents intracranial extension in the defined parameningeal
        ARMS cohort.
- category: Ophthalmologic
  name: Proptosis
  description: >-
    Orbital rhabdomyosarcoma can present with eyelid edema followed by
    proptosis. The cited cohort includes both pediatric and adult orbital RMS
    and does not establish an ARMS-specific frequency.
  phenotype_term:
    preferred_term: Proptosis
    term:
      id: HP:0000520
      label: Proptosis
  evidence:
  - reference: PMID:39792629
    reference_title: "Adult and pediatric orbital rhabdomyosarcoma: comparison of characteristics and outcomes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients in both groups presented with eyelid edema followed by proptosis with similar symptom duration (p = 0.31)."
    explanation: >-
      Supports proptosis in orbital RMS; no ARMS-specific frequency is inferred
      from this mixed-histology cohort.
- category: Systemic
  name: Metastatic Disease
  description: >-
    Metastasis and recurrence are major clinical features of fusion-positive
    ARMS. Their incidence varies by fusion status, primary site, stage, and
    ascertainment time, so this entry does not assign a single frequency band.
  evidence:
  - reference: PMID:41131073
    reference_title: Cancer-associated fibroblasts promote tumor progression in fusion-positive rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The PAX3/PAX7-FOXO1 fusion-positive alveolar subtype has poor clinical
      outcomes, with frequent recurrence, metastasis, and low survival.
    explanation: >-
      Supports recurrence and metastasis specifically in fusion-positive ARMS
      without extrapolating a mixed-RMS cohort percentage to this disorder.
  - reference: PMID:32044412
    reference_title: Patterns of Failure in Parameningeal Alveolar Rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All 7 patients with distant metastases as the first site of recurrence had
      central nervous system metastases.
    explanation: >-
      Adds direct human-cohort evidence for distant metastatic recurrence in
      pediatric parameningeal ARMS without extrapolating a page-wide frequency.
- category: Oncologic
  name: Regional Nodal Disease
  description: >-
    Regional lymph-node involvement is a clinically important staging and
    prognostic feature in ARMS. The cited cohort is limited to parameningeal
    disease; no page-wide frequency is assigned. No sufficiently specific HPO
    term for regional nodal metastasis is used in place of the broader
    lymphadenopathy phenotype.
  evidence:
  - reference: PMID:32044412
    reference_title: Patterns of Failure in Parameningeal Alveolar Rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      N1 disease and intracranial extension (ICE) portended inferior overall
      survival (P = .002 and .02, respectively).
    explanation: >-
      Directly supports regional node-positive disease as an adverse feature in
      a pediatric parameningeal ARMS cohort.
- category: Neurologic
  name: Intracranial Extension
  description: >-
    Intracranial extension occurs in a subset of parameningeal ARMS and is an
    adverse prognostic feature. This site-specific cohort estimate is not
    generalized to ARMS at other primary sites, and no overly broad HPO term is
    assigned.
  evidence:
  - reference: PMID:32044412
    reference_title: Patterns of Failure in Parameningeal Alveolar Rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most patients had group III (96%), node-negative (67%), positive FOX
      fusion status (63%) disease, and intracranial extension (54%).
    explanation: >-
      Directly quantifies intracranial extension in the defined pediatric
      parameningeal ARMS cohort.
biochemical:
- name: PAX-FOXO1 Fusion Detection
  notes: >-
    RT-PCR, FISH, or next-generation sequencing detection of PAX3-FOXO1 or
    PAX7-FOXO1 fusion is diagnostic and prognostic. Fusion status is more
    predictive of outcome than histologic classification.
  evidence:
  - reference: PMID:39686893
    reference_title: "[Characteristics of the cytogenetic variants of alveolar rhabdomyosarcoma]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Thirty-two tumor samples were collected and analyzed using a combination of histological, immunohistochemistry (Myogenin, MyoD1), and molecular genetic techniques (fluorescence in situ hybridization (FISH) and real-time polymerase chain reaction (RT-PCR))."
    explanation: Directly supports use of FISH and RT-PCR for routine PAX-FOXO1 fusion detection in clinical ARMS pathology.
- name: Myogenic Markers
  notes: >-
    Immunohistochemistry shows expression of myogenic markers including
    myogenin and MyoD1 and is interpreted together with morphology and
    molecular testing. The cited study does not by itself quantify staining
    intensity or establish a stand-alone subtype rule.
  evidence:
  - reference: PMID:39686893
    reference_title: "[Characteristics of the cytogenetic variants of alveolar rhabdomyosarcoma]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Thirty-two tumor samples were collected and analyzed using a combination of histological, immunohistochemistry (Myogenin, MyoD1), and molecular genetic techniques"
    explanation: Directly supports use of myogenin and MyoD1 immunohistochemistry as standard diagnostic markers in ARMS.
- name: Baseline circulating tumor DNA
  notes: >-
    Fusion-junction sequencing detects pretreatment ctDNA in a subset of
    fusion-positive intermediate-risk RMS. Detection is prognostic at the cohort
    level but is not yet represented here as a stand-alone diagnostic test or a
    validated treatment-selection surrogate.
  evidence:
  - reference: DOI:10.1200/jco.22.00409
    reference_title: "Circulating Tumor DNA Is Prognostic in Intermediate-Risk Rhabdomyosarcoma: A Report From the Children's Oncology Group"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Identification of pathognomonic translocations between PAX3 or PAX7 and
      FOXO1 by Rhabdo-Seq was the best method for measuring ctDNA in FP-RMS and
      detected ctDNA in 27 of 49 cases (55%).
    explanation: >-
      Directly supports fusion-junction ctDNA detection in a clinical FP-RMS
      cohort.
  - reference: DOI:10.1200/jco.22.00409
    reference_title: "Circulating Tumor DNA Is Prognostic in Intermediate-Risk Rhabdomyosarcoma: A Report From the Children's Oncology Group"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      as did patients with FP-RMS (event-free survival, 37% v 70%; P = .045;
      overall survival, 39.2% v 75%; P = .023).
    explanation: >-
      Supports prognostic association in fusion-positive RMS while not claiming
      independent significance in the smaller FP-RMS subgroup.
- name: Elevated serum lactate dehydrogenase
  notes: >-
    Elevated LDH at diagnosis was associated with worse survival in a
    resource-limited pediatric RMS cohort containing both embryonal and alveolar
    tumors. It is therefore a nonspecific prognostic laboratory finding, not an
    ARMS diagnostic marker or an ARMS-specific frequency estimate.
  evidence:
  - reference: PMID:40790568
    reference_title: Predictors of survival among children and adolescents with rhabdomyosarcoma treated in a single resource-limited centre -Uganda.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      elevated serum lactate dehydrogenase at diagnosis above 400 U/L
      (HR = 2.80; 95% CI 1.46-5.33; p = 0.002)
    explanation: >-
      Directly supports elevated baseline LDH as an adverse prognostic finding
      in the mixed-histology pediatric RMS cohort.
diagnosis:
- name: Histologic and immunohistochemical classification
  description: >-
    Tissue diagnosis evaluates the contemporary alveolar or solid-sheet
    morphology and myogenic differentiation markers. Morphology establishes
    the histologic class, while myogenin and MyoD1 support rhabdomyoblastic
    differentiation.
  diagnosis_term:
    preferred_term: immunohistochemistry
    term:
      id: NCIT:C23020
      label: Immunohistochemistry Staining Method
  markers: Myogenin; MyoD1
  results: Alveolar architecture or solid sheets of monotonous round cells with myogenic-marker expression
  evidence:
  - reference: PMID:28058850
    reference_title: Molecular diagnostics in the management of rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The current histologic definition of ARMS requires that the majority of a
      tumor show alveolar histology, or solid sheets of cells with monotonous
      round nuclei characteristic of ARMS.
    explanation: Defines the contemporary histologic classification criterion.
  - reference: PMID:39686893
    reference_title: "[Characteristics of the cytogenetic variants of alveolar rhabdomyosarcoma]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Thirty-two tumor samples were collected and analyzed using a combination
      of histological, immunohistochemistry (Myogenin, MyoD1), and molecular
      genetic techniques
    explanation: >-
      Supports the combined morphology, myogenic-marker, and molecular workflow
      in a clinical ARMS series.
- name: PAX3/7-FOXO1 fusion testing
  description: >-
    FISH, RT-PCR, or sequencing is used to establish FOXO1 rearrangement and
    identify the fusion partner. Fusion status refines prognosis and treatment
    stratification but does not replace the histologic classification.
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  markers: PAX3-FOXO1; PAX7-FOXO1; FOXO1 rearrangement
  results: Fusion-positive, fusion-negative, or alternative PAX fusion
  evidence:
  - reference: PMID:28058850
    reference_title: Molecular diagnostics in the management of rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The PAX3-FOXO1 and PAX7-FOXO1 gene fusions occur in 80% of cases with the
      alveolar subtype and are more predictive of outcome than histologic
      classification.
    explanation: >-
      Supports routine ascertainment of fusion status for molecular and
      prognostic classification.
  - reference: PMID:39686893
    reference_title: "[Characteristics of the cytogenetic variants of alveolar rhabdomyosarcoma]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Cytogenetic analysis using the FISH technique with a FOXO1-specific probe
      identified 26 (81%) samples with rearrangements at the FOXO1 locus and
      seven (19%) without rearrangements.
    explanation: Directly supports FOXO1 FISH testing in a clinical ARMS cohort.
differential_diagnoses:
- name: Embryonal rhabdomyosarcoma
  description: >-
    ERMS shares skeletal-muscle differentiation and can overlap clinically with
    ARMS. Fusion-negative tumors called ARMS by morphology frequently resemble
    ERMS molecularly and clinically, so morphology and fusion status must be
    reported separately.
  disease_term:
    preferred_term: embryonal rhabdomyosarcoma
    term:
      id: MONDO:0009993
      label: embryonal rhabdomyosarcoma
  distinguishing_features:
  - Predominantly alveolar architecture or monotonous solid-sheet cytology supports ARMS histology.
  - A PAX3-FOXO1 or PAX7-FOXO1 fusion supports fusion-positive RMS biology and adverse-risk stratification.
  - Fusion-negative alveolar histology has molecular and clinical behavior closer to ERMS.
  evidence:
  - reference: PMID:28058850
    reference_title: Molecular diagnostics in the management of rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Further, gene expression profiling of RMS shows ARMSn is highly similar
      to ERMS
    explanation: >-
      Supports the important molecular overlap between fusion-negative
      alveolar-histology RMS and ERMS.
  - reference: PMID:28058850
    reference_title: Molecular diagnostics in the management of rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Historically, pediatric RMS has been classified into two groups;
      alveolar RMS (ARMS) composed of primitive monotonous round cells typically
      with scant cytoplasm, and embryonal RMS (ERMS) with a range of appearances
      from small moderately pleomorphic cells to spindle cells that can have
      abundant eosinophilic cytoplasm with striations.
    explanation: Directly states the principal histologic distinction.
- name: B-lymphoblastic lymphoma
  description: >-
    An orbital lymphoblastic lymphoma can mimic the clinical and radiologic
    presentation of orbital rhabdomyosarcoma. Tissue histopathology and
    lineage-directed immunophenotyping distinguish the entities. The evidence
    is a single pediatric case and establishes a diagnostic pitfall rather than
    its frequency in an ARMS population.
  disease_term:
    preferred_term: lymphoblastic lymphoma
    term:
      id: MONDO:0000873
      label: lymphoblastic lymphoma
  distinguishing_features:
  - Lymphoid-lineage immunophenotyping supports B-lymphoblastic lymphoma.
  - Myogenin and MyoD1 expression with appropriate morphology supports rhabdomyosarcoma.
  - FOXO1 rearrangement testing further resolves fusion-positive RMS biology.
  evidence:
  - reference: PMID:41986061
    reference_title: "Primary orbital B cell lymphoblastic lymphoma in a toddler mimicking rhabdomyosarcoma: a diagnostic challenge."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Due to overlapping clinical and radiological features, these cases are
      often misdiagnosed initially, with rhabdomyosarcoma being a common
      provisional diagnosis.
    explanation: >-
      Directly supports orbital B-lymphoblastic lymphoma as a clinical and
      radiologic mimic requiring tissue lineage confirmation.
genetic:
- name: PAX3-FOXO1 Fusion
  association: Somatic Fusion Oncogene
  gene_term:
    preferred_term: PAX3
    term:
      id: hgnc:8617
      label: PAX3
  notes: >-
    The t(2;13)(q35;q14) translocation creates the PAX3-FOXO1 fusion and is
    the dominant FOXO1-rearranged subtype, reported in roughly 70-90% of
    fusion-positive cases. This is the most aggressive molecular subtype.
  evidence:
  - reference: PMID:39686893
    reference_title: "[Characteristics of the cytogenetic variants of alveolar rhabdomyosarcoma]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "According to literature data, the frequency of the PAX3::FOXO1 translocation is 70-90% and the PAX7::FOXO1 translocation 10-30%."
    explanation: Supports PAX3-FOXO1 as the dominant fusion-positive subtype in alveolar rhabdomyosarcoma.
- name: PAX7-FOXO1 Fusion
  association: Somatic Fusion Oncogene
  gene_term:
    preferred_term: PAX7
    term:
      id: hgnc:8621
      label: PAX7
  notes: >-
    The t(1;13)(p36;q14) translocation creates the PAX7-FOXO1 fusion in
    roughly 10-30% of fusion-positive cases. Associated with better prognosis
    than PAX3-FOXO1.
  evidence:
  - reference: PMID:39686893
    reference_title: "[Characteristics of the cytogenetic variants of alveolar rhabdomyosarcoma]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "According to literature data, the frequency of the PAX3::FOXO1 translocation is 70-90% and the PAX7::FOXO1 translocation 10-30%."
    explanation: Supports PAX7-FOXO1 as a recurrent minority fusion-positive subtype in alveolar rhabdomyosarcoma.
  - reference: PMID:22454413
    reference_title: PAX3/FOXO1 fusion gene status is the key prognostic molecular marker in rhabdomyosarcoma and significantly improves current risk stratification.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Among nonmetastatic patients, patients who were PAX3/FOXO1 positive had a
      significantly poorer outcome compared with both alveolar-negative and
      PAX7/FOXO1-positive patients.
    explanation: >-
      Supports the relative prognostic statement for the PAX7-FOXO1 fusion.
- name: MYCN Amplification
  association: Secondary Genetic Event
  gene_term:
    preferred_term: MYCN
    term:
      id: hgnc:7559
      label: MYCN
  notes: >-
    MYCN amplification occurs in a subset of fusion-positive ARMS and is
    associated with worse prognosis.
  evidence:
  - reference: PMID:24436047
    reference_title: Comprehensive genomic analysis of rhabdomyosarcoma reveals a landscape of alterations affecting a common genetic axis in fusion-positive and fusion-negative tumors.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Amplification of 2p24 involving MYCN (5%) occurred predominantly in PFP
      tumors (8 PFP vs. 1 PFN)
    explanation: >-
      Documents recurrent MYCN amplification occurring predominantly in
      fusion-positive (PFP) rhabdomyosarcoma as a cooperating genetic event.
- name: CDK4 Amplification
  association: Secondary Genetic Event
  gene_term:
    preferred_term: CDK4
    term:
      id: hgnc:1773
      label: CDK4
  notes: >-
    The gene-rich 12q13-q14 amplicon in ARMS includes CDK4 as an oncogenic
    target. Amplification is a cooperating event rather than the defining
    PAX-FOXO1 driver, and its treatment-predictive value remains complex.
  evidence:
  - reference: PMID:41828638
    reference_title: "Gene Amplification in Rhabdomyosarcoma: Lessons from a Rare Cancer."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      amplification of the 12q13-q14 chromosomal region involves a gene-rich
      region in which there are at least two critical protein-coding oncogenic
      targets (CDK4 and SHMT2).
    explanation: >-
      Directly supports CDK4 as an oncogenic target of the recurrent
      12q13-q14 amplification in ARMS.
treatments:
- name: Multi-Agent Chemotherapy
  description: >-
    Intensive chemotherapy with vincristine, actinomycin D, and cyclophosphamide
    (VAC) forms the North American backbone of treatment.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Combination Chemotherapy
    term:
      id: NCIT:C191
      label: Combination Chemotherapy
    therapeutic_agent:
    - preferred_term: vincristine
      term:
        id: CHEBI:28445
        label: vincristine
    - preferred_term: actinomycin D
      term:
        id: CHEBI:27666
        label: actinomycin D
    - preferred_term: cyclophosphamide
      term:
        id: CHEBI:4026
        label: cyclophosphamide hydrate
  regimen_term:
    preferred_term: VAC regimen
    term:
      id: NCIT:C67299
      label: VAC Regimen
  evidence:
  - reference: PMID:41038289
    reference_title: Towards directed therapy for fusion-positive rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Although the gene fusions PAX3::FOXO1 and PAX7::FOXO1 were discovered in
      the early 1990s, and since that time shown to be the molecular drivers of
      the disease, the best treatment to date still remains VAC (vincristine,
      actinomycin D, cyclophosphamide) combination therapy, first instituted as
      standard of care in the 1970s.
    explanation: >-
      Directly supports the named VAC backbone in fusion-positive RMS rather
      than only the nonspecific statement that therapy is intensive.
- name: European IVA Induction Chemotherapy
  description: >-
    Ifosfamide, vincristine, and actinomycin D (IVA) is the European induction
    backbone for high-risk localized RMS. Evidence is RMS-wide and includes
    ARMS; it does not establish superiority over VAC.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Combination Chemotherapy
    term:
      id: NCIT:C191
      label: Combination Chemotherapy
    therapeutic_agent:
    - preferred_term: ifosfamide
      term:
        id: CHEBI:5864
        label: ifosfamide
    - preferred_term: vincristine
      term:
        id: CHEBI:28445
        label: vincristine
    - preferred_term: actinomycin D
      term:
        id: CHEBI:27666
        label: actinomycin D
  evidence:
  - reference: PMID:41038289
    reference_title: Towards directed therapy for fusion-positive rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      IVA remains the standard induction regimen for high-risk localized RMS in
      Europe
    explanation: >-
      Directly supports the European IVA induction backbone while preserving
      the review-level evidence classification.
- name: Vinorelbine and Low-Dose Cyclophosphamide Maintenance
  description: >-
    Six cycles of intravenous vinorelbine plus continuous daily low-dose oral
    cyclophosphamide after remission-producing standard treatment improved
    overall survival in the EpSSG RMS 2005 randomized phase III trial. Eligible
    high-risk groups included nonmetastatic ARMS; this is a European standard
    and not an ARMS-only trial result.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Combination Chemotherapy
    term:
      id: NCIT:C191
      label: Combination Chemotherapy
    therapeutic_agent:
    - preferred_term: vinorelbine
      term:
        id: CHEBI:480999
        label: vinorelbine
    - preferred_term: cyclophosphamide
      term:
        id: CHEBI:4027
        label: cyclophosphamide
  evidence:
  - reference: PMID:31562043
    reference_title: "Vinorelbine and continuous low-dose cyclophosphamide as maintenance chemotherapy in patients with high-risk rhabdomyosarcoma (RMS 2005): a multicentre, open-label, randomised, phase 3 trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      those with non-metastatic alveolar rhabdomyosarcoma but without nodal
      involvement. Patients in remission after standard treatment
    explanation: >-
      Directly documents inclusion of nonmetastatic ARMS in the phase III
      maintenance trial.
  - reference: PMID:31562043
    reference_title: "Vinorelbine and continuous low-dose cyclophosphamide as maintenance chemotherapy in patients with high-risk rhabdomyosarcoma (RMS 2005): a multicentre, open-label, randomised, phase 3 trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      5-year overall survival was 86·5% (95% CI 80·2-90·9) with maintenance
      chemotherapy versus 73·7% (65·8-80·1) without
    explanation: >-
      Directly supports the randomized overall-survival benefit; the
      disease-free-survival endpoint did not cross its significance threshold.
- name: Cixutumumab or Temozolomide Intensification
  description: >-
    COG ARST08P1 evaluated adding either cixutumumab or temozolomide to an
    intensive metastatic-RMS chemotherapy backbone. Both nonrandomized pilot
    regimens were feasible but neither improved outcome; they are retained as
    negative clinical evidence and are not presented as standards of care.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  evidence:
  - reference: PMID:30351457
    reference_title: "The addition of cixutumumab or temozolomide to intensive multiagent chemotherapy is feasible but does not improve outcome for patients with metastatic rhabdomyosarcoma: A report from the Children's Oncology Group."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Neither agent improved outcome compared with the same chemotherapy that
      was used on ARST0431.
    explanation: >-
      Directly refutes clinical benefit from either intensification strategy in
      the metastatic RMS pilot cohorts, most of which had alveolar histology.
- name: Surgical Resection
  description: >-
    Complete surgical resection with negative margins when feasible without
    excessive morbidity. Surgery may be delayed until after chemotherapy
    to facilitate resection.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Definitive Surgical Resection
    term:
      id: NCIT:C154430
      label: Definitive Surgical Resection
  evidence:
  - reference: PMID:39809723
    reference_title: Rhabdomyosarcoma Surgical Update.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Advances in local control therapy of RMS have improved outcomes after surgical resection of the primary tumor, either before or after induction chemotherapy, even in the setting of metastatic disease."
    explanation: Supports surgical resection as an established local-control modality in rhabdomyosarcoma, including after induction chemotherapy.
- name: Radiation Therapy
  description: >-
    Radiation therapy is used for local control, particularly when complete
    surgical resection is not possible or margins are positive.
  therapeutic_modality: RADIOTHERAPY
  treatment_term:
    preferred_term: Radiation Therapy
    term:
      id: NCIT:C15313
      label: Radiation Therapy
  evidence:
  - reference: PMID:32124549
    reference_title: "Do children and adolescents with completely resected alveolar rhabdomyosarcoma require adjuvant radiation? A report from the Children's Oncology Group."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with FOXO1 positivity who received RT had superior EFS compared with those who did not (77.8% vs 16.7%; P = 0.03)."
    explanation: Supports adjuvant radiation therapy in FOXO1-positive alveolar rhabdomyosarcoma, even after complete resection.
- name: PAX-FOXO1/ETS1 Complex Disruption
  description: >-
    Investigational small-molecule disruption of the PAX3-FOXO1/ETS1 complex is
    a direct chromatin-handle strategy: it aims to displace PAX3-FOXO1 from
    disease enhancers and suppress fusion-dependent gene regulation rather than
    treating the fusion as an untargetable upstream abstraction.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: YK-4-279
      term:
        id: CHEBI:94301
        label: YK-4-279
  evidence:
  - reference: PMID:39448867
    reference_title: Dependence of PAX3-FOXO1 chromatin occupancy on ETS1 at important disease-promoting genes exposes new targetable vulnerability in Fusion-Positive Rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We further show that the PAX3-FOXO1/ETS1 complex can be disrupted by the
      clinically relevant small molecule inhibitor YK-4-279.
    explanation: >-
      Supports YK-4-279-like disruption of the PAX3-FOXO1/ETS1 complex as an
      investigational therapeutic mechanism.
  target_mechanisms:
  - target: ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module
    treatment_effect: INHIBITS
    description: >-
      Disrupts the ETS1-dependent PAX3-FOXO1 chromatin complex and thereby
      reduces fusion occupancy and target-gene regulation.
    evidence:
    - reference: PMID:39448867
      reference_title: Dependence of PAX3-FOXO1 chromatin occupancy on ETS1 at important disease-promoting genes exposes new targetable vulnerability in Fusion-Positive Rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        YK-4-279 displaces PAX3-FOXO1 from chromatin and interferes with
        PAX3-FOXO1-dependent gene regulation, resulting in potent inhibition of
        growth and invasive properties in FP-RMS, along with downregulation of
        FGF8, IL4R, MEST and PODXL expression.
      explanation: >-
        Shows that the compound acts at the modeled ETS1/PAX3-FOXO1 chromatin
        cofactor node and suppresses downstream malignant behavior.
- name: YOD1 Inhibition
  description: >-
    Investigational YOD1 inhibition is modeled as a feedback-loop intervention:
    inhibiting YOD1 destabilizes both PAX-FOXO1 and N-Myc, reducing the
    reciprocal oncogenic amplification loop rather than targeting only a
    downstream proliferation phenotype.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  evidence:
  - reference: PMID:41401084
    reference_title: Therapeutic targeting of YOD1 disrupts the PAX-FOXO1/N-Myc feedback loop in rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Knocking down YOD1 or inhibiting it with G5 could suppress FP-RMS growth
      both in vitro and in vivo, through promoting the degradation of both
      PAX-FOXO1 and N-Myc.
    explanation: >-
      Supports YOD1 inhibition as a preclinical strategy that destabilizes both
      oncogenic proteins and suppresses FP-RMS growth.
  target_mechanisms:
  - target: YOD1-N-Myc PAX-FOXO1 Feedback Loop
    treatment_effect: INHIBITS
    description: >-
      Inhibits YOD1-mediated stabilization of PAX-FOXO1 and N-Myc, collapsing
      the positive feedback loop.
    evidence:
    - reference: PMID:41401084
      reference_title: Therapeutic targeting of YOD1 disrupts the PAX-FOXO1/N-Myc feedback loop in rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Knocking down YOD1 or inhibiting it with G5 could suppress FP-RMS
        growth both in vitro and in vivo, through promoting the degradation of
        both PAX-FOXO1 and N-Myc.
      explanation: >-
        Directly supports the treatment-mechanism link between YOD1 inhibition
        and disruption of the modeled feedback loop.
- name: FGFR Inhibitor Therapy
  description: >-
    Investigational FGFR-directed therapy may be relevant in fusion-positive
    ARMS with high FGFR4/FGF8 signaling activity. Preclinical models and early
    translational evidence support FGFR4-selective and multikinase FGFR
    inhibition as precision-therapy approaches in this molecular subset.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: FGF401 (roblitinib)
      term:
        id: NCIT:C120102
        label: Roblitinib
    - preferred_term: lenvatinib
      term:
        id: CHEBI:85994
        label: lenvatinib
  evidence:
  - reference: PMID:42041178
    reference_title: Comprehensive Multiplatform Tyrosine Kinase Profiling Reveals Novel Actionable FGFR Aberrations across Sarcomas Affecting the Young.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We demonstrate marked tumor growth inhibition in all FP-RMS PDXs
      treated with single-agent FGF401 (FGFR4-specific inhibitor) and
      single-agent lenvatinib (multikinase FGFR inhibitor)
    explanation: >-
      Supports preclinical FGFR-directed efficacy in fusion-positive RMS
      patient-derived xenograft models.
  - reference: PMID:42041178
    reference_title: Comprehensive Multiplatform Tyrosine Kinase Profiling Reveals Novel Actionable FGFR Aberrations across Sarcomas Affecting the Young.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      report a clinical response to lenvatinib in a patient with relapsed
      metastatic FP-RMS.
    explanation: >-
      Supports an early human clinical response signal for FGFR-directed
      therapy in relapsed metastatic fusion-positive RMS.
  target_mechanisms:
  - target: FGFR-Driven RTK Signaling
    treatment_effect: INHIBITS
    description: >-
      FGFR4-selective and multikinase FGFR inhibitors block the upstream
      receptor tyrosine kinase node, not the downstream RAS/PI3K effector arm;
      RAS- or PIK3CA-level alterations therefore predict potential resistance.
    evidence:
    - reference: PMID:42041178
      reference_title: Comprehensive Multiplatform Tyrosine Kinase Profiling Reveals Novel Actionable FGFR Aberrations across Sarcomas Affecting the Young.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        We demonstrate marked tumor growth inhibition in all FP-RMS PDXs
        treated with single-agent FGF401 (FGFR4-specific inhibitor) and
        single-agent lenvatinib (multikinase FGFR inhibitor)
      explanation: >-
        FGFR-directed agents act at the FGFR4 receptor tyrosine kinase node,
        the upstream step now represented separately from the RAS/PI3K arm.
- name: Histone Deacetylase Inhibitor Therapy
  description: >-
    Investigational class I histone deacetylase inhibition, exemplified by
    entinostat in PAX3::FOXO1-positive ARMS PDX models, targets the
    HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 chemotherapy-resistance circuit and may
    resensitize relapsed or resistant disease to RMS chemotherapy.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: entinostat
      term:
        id: CHEBI:132082
        label: entinostat
  evidence:
  - reference: PMID:39147820
    reference_title: Entinostat as a combinatorial therapeutic for rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We identified single agent, additive or synergistic relationships between
      relapse-specific chemotherapies and clinically relevant drug exposures of
      entinostat in three PAX3::FOXO1+ ARMS mouse models.
    explanation: >-
      Supports entinostat as a preclinical combination strategy in
      PAX3::FOXO1-positive ARMS models.
  target_mechanisms:
  - target: HDAC3-SMARCA4-miR-27a Chemotherapy Resistance Circuit
    treatment_effect: INHIBITS
    description: >-
      HDAC inhibition is modeled as acting on the HDAC3-SMARCA4-miR-27a
      checkpoint-adaptation circuit that mediates chemotherapy resistance.
    evidence:
    - reference: PMID:39147820
      reference_title: Entinostat as a combinatorial therapeutic for rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Chemotherapy resistance in ARMS has previously been attributed to
        PAX3::FOXO1-mediated cell cycle checkpoint adaptation, which is
        mediated by an HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit that can be
        disrupted by HDAC3 inhibition.
      explanation: >-
        Directly links HDAC3 inhibition to disruption of the modeled
        chemotherapy-resistance circuit.
clinical_trials:
- name: NCT02567435
  phase: PHASE_III
  status: ACTIVE_NOT_RECRUITING
  description: >-
    Children's Oncology Group ARST1431 compares VAC alternating with
    vincristine/irinotecan against the same chemotherapy plus temsirolimus in
    intermediate-risk RMS. Alveolar rhabdomyosarcoma is an eligible condition;
    the registry is not an ARMS-only efficacy study.
  evidence:
  - reference: clinicaltrials:NCT02567435
    reference_title: A Randomized Phase 3 Study of Vincristine, Dactinomycin, Cyclophosphamide (VAC) Alternating With Vincristine and Irinotecan (VI) Versus VAC/VI Plus Temsirolimus (TORI, Torisel, NSC# 683864) in Patients With Intermediate Risk (IR) Rhabdomyosarcoma (RMS)
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This randomized phase III trial studies how well combination chemotherapy
      (vincristine sulfate, dactinomycin, cyclophosphamide alternated with
      vincristine sulfate and irinotecan hydrochloride or vinorelbine) works
      compared to combination chemotherapy plus temsirolimus in treating
      patients with rhabdomyosarcoma
    explanation: >-
      The ClinicalTrials.gov record directly documents the phase III
      intermediate-risk RMS comparison; it is not interpreted as proof of
      benefit before results are available.
animal_models:
- species: Mus musculus
  genotype: Patient-derived xenografts of PAX3-FOXO1 fusion-positive rhabdomyosarcoma
  category: Patient-derived xenograft
  description: >-
    Fusion-positive RMS PDXs preserve patient-tumor context for testing the
    FGFR4-selective inhibitor roblitinib and multikinase inhibitor lenvatinib.
    They support preclinical response, not population-level clinical efficacy.
  evidence:
  - reference: PMID:42041178
    reference_title: Comprehensive Multiplatform Tyrosine Kinase Profiling Reveals Novel Actionable FGFR Aberrations across Sarcomas Affecting the Young.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We demonstrate marked tumor growth inhibition in all FP-RMS PDXs treated
      with single-agent FGF401 (FGFR4-specific inhibitor) and single-agent
      lenvatinib (multikinase FGFR inhibitor)
    explanation: >-
      Directly establishes the FP-RMS PDX treatment model and its preclinical
      response endpoint.
- species: Mus musculus
  genotype: PAX3::FOXO1-positive alveolar rhabdomyosarcoma mouse and PDX models
  category: Genetically engineered and patient-derived tumor models
  description: >-
    Three PAX3::FOXO1-positive ARMS mouse models were used to test entinostat at
    clinically relevant exposure alone and with relapse-directed chemotherapy.
    Model-specific synergy does not establish human efficacy.
  evidence:
  - reference: PMID:39147820
    reference_title: Entinostat as a combinatorial therapeutic for rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We identified single agent, additive or synergistic relationships between
      relapse-specific chemotherapies and clinically relevant drug exposures of
      entinostat in three PAX3::FOXO1+ ARMS mouse models.
    explanation: Directly defines the number, genotype, intervention, and use of the models.
experimental_models:
- name: Patient-derived ARMS single-cell culture model
  experimental_model_type: PRIMARY_CELL_CULTURE
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  tissue_term:
    preferred_term: skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  cell_types:
  - preferred_term: skeletal muscle myoblast
    term:
      id: CL:0000515
      label: skeletal muscle myoblast
  cell_source: Patient-derived primary RMS cultures
  culture_system: Primary tumor culture profiled by single-cell RNA sequencing, mass cytometry, and high-content imaging
  publication: PMID:36753540
  description: >-
    Patient-derived aRMS cultures resolve cycling progenitor, muscle stem-like,
    and differentiated states and enable perturbational testing of RAF/MEK
    inhibitors. Culture-state findings require confirmation in clinical tumors.
  modeled_mechanisms:
  - target: Blocked Myogenic Differentiation
    description: Tests whether tumor-cell states can be redirected toward myogenic differentiation.
    evidence:
    - reference: PMID:36753540
      reference_title: Single-cell profiling of alveolar rhabdomyosarcoma reveals RAS pathway inhibitors as cell-fate hijackers with therapeutic relevance.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        We screened for drugs hijacking aRMS toward clinically favorable
        subpopulations and identified a combination of RAF and MEK inhibitors
        that potently induces myogenic differentiation and inhibits tumor
        growth.
      explanation: Directly links the culture model to the differentiation mechanism and perturbation.
  evidence:
  - reference: PMID:36753540
    reference_title: Single-cell profiling of alveolar rhabdomyosarcoma reveals RAS pathway inhibitors as cell-fate hijackers with therapeutic relevance.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Here, we combined single-cell RNA sequencing, mass cytometry, and
      high-content imaging to resolve intratumoral heterogeneity of
      patient-derived primary RMS cultures.
    explanation: Directly establishes the experimental system and assay suite.
- name: Fusion-positive RMS cancer-associated fibroblast coculture
  experimental_model_type: CO_CULTURE
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_types:
  - preferred_term: cancer-associated fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  - preferred_term: skeletal muscle myoblast
    term:
      id: CL:0000515
      label: skeletal muscle myoblast
  cell_source: Metastatic fusion-positive RMS-derived fibroblasts and fusion-positive RMS tumor cells
  culture_system: Tumor-cell and fibroblast conditioned-medium/coculture model
  publication: PMID:41131073
  description: >-
    A human coculture model tests fibroblast-secreted support of FP-RMS growth,
    migration, immune-checkpoint expression, and cyclophosphamide resistance.
    It represents one metastatic microenvironment and does not establish the
    prevalence of this state across patients.
  modeled_mechanisms:
  - target: Immune-Evasive Tumor Microenvironment
    description: Tests CAF-mediated growth and treatment-resistance effects.
    evidence:
    - reference: PMID:41131073
      reference_title: Cancer-associated fibroblasts promote tumor progression in fusion-positive rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        The cancer-associated fibroblasts also promoted expression of immune
        checkpoints and conferred resistance to cyclophosphamide, a chemotherapy
        commonly used to treat this disease.
      explanation: Directly supports the immune-checkpoint and resistance outputs of the coculture model.
  evidence:
  - reference: PMID:41131073
    reference_title: Cancer-associated fibroblasts promote tumor progression in fusion-positive rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      This study establishes a model of cancer-associated fibroblasts from
      metastatic fusion-positive rhabdomyosarcoma.
    explanation: Directly establishes the disease-specific fibroblast model.
discussions:
- discussion_id: gap_arms_pax_foxo1_dependency_hierarchy
  prompt: >-
    Which upstream or feedback-maintenance mechanism is required for the
    fusion-dependent regulatory program that produces the ARMS-specific
    open-chromatin signature, and can any chemical or genetic perturbation
    phenocopy acute fusion withdrawal at that assay readout?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#PAX-FOXO1 Fusion Oncogene
  - pathophysiology#PAX-FOXO1 Disease Enhancer Reprogramming
  - pathophysiology#ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module
  - pathophysiology#YOD1-N-Myc PAX-FOXO1 Feedback Loop
  - pathophysiology#HDAC3-SMARCA4-miR-27a Chemotherapy Resistance Circuit
  - pathophysiology#Chemotherapy Resistance and Relapse
  - treatments#PAX-FOXO1/ETS1 Complex Disruption
  - treatments#YOD1 Inhibition
  - treatments#Histone Deacetylase Inhibitor Therapy
  rationale: >-
    Older work established PAX3::FOXO1 and PAX7::FOXO1 as molecular drivers, but
    a 2025 therapy review still notes that standard systemic therapy remains
    VAC despite decades of fusion knowledge. The disease model now makes the
    hidden middle explicit but should not treat open chromatin as a causal node:
    open chromatin is the observable readout of a fusion-dependent regulatory
    program. The causal candidates are upstream or feedback-maintenance
    mechanisms such as PAX-FOXO1 protein abundance, ETS1/KDM3A cofactor
    occupancy, and YOD1/N-Myc stabilization. HDAC3-SMARCA4-miR-27a is better
    treated as a chemotherapy-resistance branch, and FGFR4/FGF8 signaling is
    better treated as a downstream output or feedback-control test, unless
    perturbation proves that either one feeds back onto the regulatory program.
    Forward curation through 2024-2026 provides partial therapeutic handles for
    those layers, but does not yet establish which handle changes the
    disease-defining regulatory state rather than only improving a downstream
    phenotype in one model context.
  proposed_experiments:
  - experiment_id: exp_arms_isogenic_pax_foxo1_dependency_prioritization
    name: ARMS regulatory-state dependency screen using open chromatin as readout
    description: >-
      Define disease-specific open chromatin regions in matched FP-RMS models
      and use that signature as an assay readout, not as the causal mechanism.
      Perturb candidate causes of the fusion-dependent regulatory program
      first: acute PAX3-FOXO1 withdrawal, PAX3-FOXO1/ETS1 complex disruption,
      and YOD1 inhibition. Then use HDAC inhibition as a resistance-branch test
      under chemotherapy pressure and FGFR inhibition as a downstream-output
      control. Compare diagnostic-like, relapse-like, and
      chemotherapy-resistant states to determine which perturbation changes the
      regulatory-state readout and which only changes viability, signaling, or
      drug response downstream.
    experiment_type:
      preferred_term: isogenic dependency mapping experiment
    model_systems:
    - name: FP-RMS cell-line and patient-derived culture panel
      description: >-
        Human fusion-positive rhabdomyosarcoma models spanning PAX3-FOXO1 and
        PAX7-FOXO1 states, including diagnostic-like cultures and relapse- or
        chemotherapy-resistance-enriched cultures with matched baseline ATAC-seq
        or equivalent open-chromatin profiles.
      experimental_model_type: CELL_LINE
      organism:
        preferred_term: human
        term:
          id: NCBITaxon:9606
          label: Homo sapiens
      cell_types:
      - preferred_term: skeletal muscle myoblast
        term:
          id: CL:0000515
          label: skeletal muscle myoblast
      publication: PMID:41401084
      modeled_mechanisms:
      - target: PAX-FOXO1 Fusion Oncogene
        description: Provides the reference perturbation for complete fusion dependency.
      - target: PAX-FOXO1 Disease Enhancer Reprogramming
        description: >-
          Defines the latent regulatory program whose assayable projection is
          the ARMS-specific open chromatin signature.
      - target: ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module
        description: Tests whether cofactor disruption phenocopies fusion withdrawal at disease enhancers.
      - target: YOD1-N-Myc PAX-FOXO1 Feedback Loop
        description: Tests whether destabilizing the feedback loop reduces the fusion-dependent regulatory program.
      - target: HDAC3-SMARCA4-miR-27a Chemotherapy Resistance Circuit
        description: Tests a chemotherapy-resistance branch rather than baseline regulatory-state maintenance.
      - target: FGFR-Driven RTK Signaling
        description: Tests a downstream signaling output and potential feedback control, not a primary cause of open chromatin.
      - target: Chemotherapy Resistance and Relapse
        description: Measures whether regulatory-state changes predict durable suppression of resistant outgrowth.
    perturbations:
    - name: Acute PAX-FOXO1 withdrawal reference
      target: pathophysiology#PAX-FOXO1 Fusion Oncogene
      description: >-
        Degrade, silence, or inducibly withdraw the fusion protein to create the
        reference regulatory-state and open-chromatin-signature change for all
        downstream comparisons.
    - name: PAX-FOXO1/ETS1 complex disruption
      target: treatments#PAX-FOXO1/ETS1 Complex Disruption
      description: >-
        Apply YK-4-279-like complex disruption to test whether the ETS1/KDM3A
        cofactor handle collapses PAX-FOXO1 enhancer occupancy.
    - name: YOD1 feedback-loop inhibition
      target: treatments#YOD1 Inhibition
      description: >-
        Inhibit or knock down YOD1 to destabilize PAX-FOXO1 and N-Myc and test
        whether feedback-loop collapse changes the fusion-dependent regulatory
        program as measured by open chromatin and transcriptional readouts.
    - name: HDAC3 resistance-circuit inhibition
      target: treatments#Histone Deacetylase Inhibitor Therapy
      description: >-
        Treat with entinostat or a more selective HDAC3 perturbation during
        chemotherapy exposure to test whether a resistance-specific branch is
        reversed. This is not interpreted as baseline regulatory-state
        maintenance unless it also shifts the fusion-withdrawal-like ATAC and
        occupancy readouts.
    - name: FGFR pathway inhibition
      target: treatments#FGFR Inhibitor Therapy
      description: >-
        Inhibit FGFR4/FGF8 signaling as a downstream-output control. A viability
        or ERK/AKT response without an ATAC or fusion-occupancy shift would
        classify FGFR signaling as an output of the regulatory program rather
        than a maintainer of it.
    - name: Combination rescue matrix
      target: pathophysiology#Chemotherapy Resistance and Relapse
      description: >-
        Combine upstream/feedback regulatory-state perturbations with
        resistance-branch or downstream-output inhibitors to test whether
        chromatin-state rescue must be paired with suppression of resistant
        outgrowth.
    readouts:
    - name: Disease-specific open chromatin signature change
      target: pathophysiology#PAX-FOXO1 Disease Enhancer Reprogramming
      description: >-
        Measure whether disease-specific ATAC-seq peaks and enhancer activity
        shift toward the acute fusion-withdrawal or fusion-negative comparator
        state after each perturbation. The ATAC-seq peaks are the observable
        signature used to infer regulatory-state change, not a separate causal
        node in the pathograph.
      biological_processes:
      - preferred_term: chromatin remodeling
        term:
          id: GO:0006338
          label: chromatin remodeling
      - preferred_term: positive regulation of transcription by RNA polymerase II
        term:
          id: GO:0045944
          label: positive regulation of transcription by RNA polymerase II
      assays:
      - preferred_term: ATAC-seq
      - preferred_term: CUT&Tag
      - preferred_term: single-cell RNA-seq
      direction: NEGATIVE
    - name: Fusion occupancy and mechanism-specific target output
      target: pathophysiology#ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module
      description: >-
        Quantify PAX-FOXO1 and ETS1 occupancy, FGF8/IL4R/MEST/PODXL expression,
        MYCN/N-Myc expression, YOD1-dependent protein abundance, and
        HDAC3-resistance-circuit markers after each perturbation to distinguish
        causal regulatory-state change from downstream output change.
      biological_processes:
      - preferred_term: positive regulation of transcription by RNA polymerase II
        term:
          id: GO:0045944
          label: positive regulation of transcription by RNA polymerase II
      assays:
      - preferred_term: CUT&Tag
      - preferred_term: RNA sequencing
      - preferred_term: immunoblot
      direction: NEGATIVE
    - name: Differentiation and malignant-growth response
      target: pathophysiology#Blocked Myogenic Differentiation
      description: >-
        Measure myogenic differentiation, proliferation, apoptosis, and invasive
        properties after each regulatory-state perturbation or downstream-output
        control.
      biological_processes:
      - preferred_term: cell differentiation
        term:
          id: GO:0030154
          label: cell differentiation
      assays:
      - preferred_term: differentiation assay
      - preferred_term: cell viability assay
      - preferred_term: invasion assay
      direction: POSITIVE
    - name: Chemotherapy-resistance reversal
      target: pathophysiology#Chemotherapy Resistance and Relapse
      description: >-
        Quantify whether regulatory-state changes or HDAC3 resistance-branch
        inhibition predict improved chemotherapy sensitivity and suppression of
        resistant outgrowth in relapse-like models.
      biological_processes:
      - preferred_term: response to xenobiotic stimulus
        term:
          id: GO:0009410
          label: response to xenobiotic stimulus
      assays:
      - preferred_term: cell viability assay
      - preferred_term: chemotherapy response assay
      direction: NEGATIVE
    controls:
    - name: Fusion-negative RMS comparator
      description: Tests whether perturbation effects are specific to PAX-FOXO1-driven disease.
    - name: Acute fusion-withdrawal positive control
      description: Defines the expected full chromatin-collapse signature for a fusion-dependent state.
    - name: Vehicle or non-targeting perturbation controls
      description: Baseline control for drug, degron, or genetic perturbation effects.
    decision_criterion: >-
      A mechanism is classified as regulatory-state-maintaining if its chemical
      or genetic perturbation reproducibly shifts the ARMS-specific open
      chromatin signature and fusion/cofactor occupancy toward the acute
      fusion-withdrawal reference, then produces coherent downstream effects on
      differentiation, proliferation or invasion, and chemotherapy response. A
      perturbation that improves viability, signaling, or chemotherapy response
      without changing the open-chromatin and occupancy readouts is classified
      as a downstream or branch-specific therapeutic handle, not as closure of
      the core regulatory-state gap.
    would_support:
    - pathophysiology#PAX-FOXO1 Fusion Oncogene
    - pathophysiology#PAX-FOXO1 Disease Enhancer Reprogramming
    - pathophysiology#ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module
    - pathophysiology#YOD1-N-Myc PAX-FOXO1 Feedback Loop
    - pathophysiology#HDAC3-SMARCA4-miR-27a Chemotherapy Resistance Circuit
    - pathophysiology#Chemotherapy Resistance and Relapse
    - pathophysiology#Blocked Myogenic Differentiation
    - pathophysiology#Aberrant Cell Proliferation
    evidence:
    - reference: PMID:41401084
      reference_title: Therapeutic targeting of YOD1 disrupts the PAX-FOXO1/N-Myc feedback loop in rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        The reciprocal transcriptional activation of PAX3-FOXO1 and N-Myc is
        critical for FP-RMS malignancy.
      explanation: >-
        Supports inclusion of the YOD1/N-Myc feedback arm in the proposed
        dependency-prioritization experiment.
    - reference: PMID:39448867
      reference_title: Dependence of PAX3-FOXO1 chromatin occupancy on ETS1 at important disease-promoting genes exposes new targetable vulnerability in Fusion-Positive Rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        We further show that the PAX3-FOXO1/ETS1 complex can be disrupted by
        the clinically relevant small molecule inhibitor YK-4-279.
      explanation: >-
        Supports inclusion of ETS1-dependent fusion chromatin occupancy as a
        candidate targetable dependency layer.
    - reference: PMID:39147820
      reference_title: Entinostat as a combinatorial therapeutic for rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Chemotherapy resistance in ARMS has previously been attributed to
        PAX3::FOXO1-mediated cell cycle checkpoint adaptation, which is mediated
        by an HDAC3-SMARCA4-miR-27a-PAX3::FOXO1 circuit that can be disrupted by
        HDAC3 inhibition.
      explanation: >-
        Supports inclusion of the HDAC3-SMARCA4-miR-27a resistance circuit as a
        separate dependency layer in the experiment.
  evidence:
  - reference: PMID:41038289
    reference_title: Towards directed therapy for fusion-positive rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Although the gene fusions PAX3::FOXO1 and PAX7::FOXO1 were discovered in
      the early 1990s, and since that time shown to be the molecular drivers of
      the disease, the best treatment to date still remains VAC (vincristine,
      actinomycin D, cyclophosphamide) combination therapy, first instituted as
      standard of care in the 1970s.
    explanation: >-
      Shows that the therapy gap remains open despite longstanding knowledge of
      the causal fusion oncogenes.
  - reference: PMID:41401084
    reference_title: Therapeutic targeting of YOD1 disrupts the PAX-FOXO1/N-Myc feedback loop in rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      However, the oncogenic mechanisms and therapeutic strategies of PAX-FOXO1
      remain incompletely understood.
    explanation: >-
      Explicitly states that PAX-FOXO1 mechanisms and therapeutic strategies
      remain incomplete while presenting one forward partial answer.
  - reference: PMID:39448867
    reference_title: Dependence of PAX3-FOXO1 chromatin occupancy on ETS1 at important disease-promoting genes exposes new targetable vulnerability in Fusion-Positive Rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      However, details of PAX3-FOXO1 epigenetic mechanisms, including
      interactions with, and dependence on, other chromatin and transcription
      factors, are incompletely understood.
    explanation: >-
      Documents that cofactor-dependent fusion chromatin regulation remains an
      open mechanistic layer even after recent target-discovery work.
- discussion_id: gap_arms_fgfr_response_biomarkers
  prompt: >-
    Which fusion-positive ARMS tumors have disease-specific open chromatin at
    FGF8 regulatory elements that correspond to previously reported
    PAX3-FOXO1/ETS1/KDM3A-bound enhancers of FGF8, and also show high FGF8 RNA,
    high FGFR4 RNA, and FGFR4 phosphorylation, such that the tumor is clinically
    responsive to FGFR inhibition? Conversely, which tumors express some of the
    FGF8/FGFR4/FGFR4_pY signature but are not FGFR-dependent because downstream
    RAS/PI3K activation, relapse-associated adaptation, or other resistance
    circuitry bypasses FGFR signaling?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#PAX-FOXO1 Fusion Oncogene
  - pathophysiology#PAX-FOXO1 Disease Enhancer Reprogramming
  - pathophysiology#ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module
  - pathophysiology#FGFR-Driven RTK Signaling
  - pathophysiology#RAS/PI3K Effector Pathway Activation
  - treatments#FGFR Inhibitor Therapy
  rationale: >-
    Recent 2026 multiplatform profiling provides the strongest forward evidence
    that FGFR4/FGF8 coexpression with FGFR4 phosphorylation can identify
    FGFR-inhibitor-sensitive FP-RMS. The same paper frames the broader unresolved
    question: RNA overexpression alone is common, but it is not always clear
    when receptor expression marks kinase activation, signaling dependence, and
    drug response. Because the pathograph now connects FGF8 to the
    ETS1/KDM3A/PAX-FOXO1 chromatin cofactor module, the open curation problem is
    whether disease-specific open chromatin at FGF8 regulatory elements that
    correspond to PAX3-FOXO1/ETS1/KDM3A-bound enhancers of FGF8, direct
    factor-occupancy evidence where available, FGF8/FGFR4 transcript abundance,
    FGFR4 phosphorylation, and drug response form one coherent dependency
    signature or split into bypass states.
  proposed_experiments:
  - experiment_id: exp_arms_fgfr_functional_biomarker_response_panel
    name: Functional FGFR biomarker-response panel in FP-RMS
    description: >-
      Assemble FP-RMS patient samples, cell lines, organoids, and PDX-derived
      cultures stratified by ATAC-seq accessibility at FGF8 regulatory elements
      that correspond to PAX3-FOXO1/ETS1/KDM3A-bound enhancers of FGF8, by
      direct PAX3-FOXO1/ETS1/KDM3A occupancy where factor-binding data are
      available, by FGFR4 RNA, FGF8 RNA, FGFR4 phosphorylation, and
      RTK/RAS/PI3K alterations. Test FGFR4-selective and multikinase FGFR
      inhibitors alone and with downstream pathway blockade to determine which
      biomarker combinations predict response or bypass.
    experiment_type:
      preferred_term: functional precision-oncology biomarker experiment
    model_systems:
    - name: FP-RMS phosphoproteomic response panel
      description: >-
        Human fusion-positive rhabdomyosarcoma samples and derived models with
        matched transcriptomic, phosphoproteomic, genomic, and drug-response
        measurements.
      experimental_model_type: OTHER
      organism:
        preferred_term: human
        term:
          id: NCBITaxon:9606
          label: Homo sapiens
      publication: PMID:42041178
      modeled_mechanisms:
      - target: PAX-FOXO1 Disease Enhancer Reprogramming
        description: Tests whether FGFR response tracks an upstream disease-enhancer state.
      - target: ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module
        description: Tests whether FGF8/FGFR4 dependence is coupled to the modeled cofactor-occupancy branch.
      - target: FGFR-Driven RTK Signaling
        description: Tests whether FGFR4/FGF8 expression and FGFR4_pY mark active signaling dependence.
      - target: RAS/PI3K Effector Pathway Activation
        description: Tests downstream bypass when FGFR is inhibited.
    perturbations:
    - name: FGFR inhibitor challenge
      target: treatments#FGFR Inhibitor Therapy
      description: >-
        Treat models with FGFR4-selective and multikinase FGFR inhibitors to
        compare response across FGFR4 RNA, FGF8 RNA, and FGFR4_pY strata.
    - name: Downstream bypass testing
      target: pathophysiology#RAS/PI3K Effector Pathway Activation
      description: >-
        Add RAS-MAPK or PI3K-AKT pathway blockade, or analyze models with
        existing RTK/RAS/PI3K alterations, to identify FGFR-independent
        resistance states.
    readouts:
    - name: FGF8 fusion/cofactor regulatory state and FGFR response
      target: pathophysiology#ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module
      description: >-
        Quantify disease-specific open chromatin at FGF8 regulatory elements
        that correspond to PAX3-FOXO1/ETS1/KDM3A-bound enhancers of FGF8, and,
        where possible, separately quantify PAX3-FOXO1, ETS1, and KDM3A
        occupancy. Relate those chromatin-accessibility and factor-occupancy
        features to FGF8 RNA, FGFR4 RNA, and FGFR4 phosphorylation.
      biological_processes:
      - preferred_term: chromatin remodeling
        term:
          id: GO:0006338
          label: chromatin remodeling
      assays:
      - preferred_term: ATAC-seq
      - preferred_term: CUT&Tag
      - preferred_term: RNA sequencing
      direction: NEGATIVE
    - name: FGFR activation and signaling dependence
      target: pathophysiology#FGFR-Driven RTK Signaling
      description: >-
        Quantify FGFR4 phosphorylation, FGF8/FGFR4 RNA, downstream ERK/AKT
        signaling, and suppression of pathway output after FGFR inhibition.
      biological_processes:
      - preferred_term: fibroblast growth factor receptor signaling pathway
        term:
          id: GO:0008543
          label: fibroblast growth factor receptor signaling pathway
      assays:
      - preferred_term: phosphoproteomics
      - preferred_term: RNA sequencing
      direction: NEGATIVE
    - name: Drug response and bypass
      target: treatments#FGFR Inhibitor Therapy
      description: >-
        Measure tumor growth, viability, apoptosis, and pathway reactivation
        after FGFR inhibition alone or with downstream blockade.
      assays:
      - preferred_term: cell viability assay
      - preferred_term: tumor growth assay
      direction: NEGATIVE
    controls:
    - name: FGFR4-low FP-RMS controls
      description: Models lacking the candidate FGFR4/FGF8/FGFR4_pY response signature.
    - name: RAS/PI3K-altered comparator models
      description: Models expected to bypass upstream FGFR dependence.
    decision_criterion: >-
      The biomarker model is supported if disease-specific open chromatin at
      FGF8 regulatory elements corresponding to PAX3-FOXO1/ETS1/KDM3A-bound
      enhancers of FGF8, direct PAX3-FOXO1/ETS1/KDM3A occupancy where measured,
      high FGF8/FGFR4 RNA, and FGFR4 phosphorylation jointly predict
      FGFR-inhibitor response and pathway suppression, while discordant,
      RAS/PI3K-altered, or
      relapse/resistance-enriched models show bypass or require combination
      downstream blockade.
    would_support:
    - pathophysiology#ETS1-KDM3A PAX-FOXO1 Chromatin Cofactor Module
    - pathophysiology#FGFR-Driven RTK Signaling
    - treatments#FGFR Inhibitor Therapy
    would_refute:
    - pathophysiology#FGFR-Driven RTK Signaling
    evidence:
    - reference: PMID:42041178
      reference_title: Comprehensive Multiplatform Tyrosine Kinase Profiling Reveals Novel Actionable FGFR Aberrations across Sarcomas Affecting the Young.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        We demonstrate marked tumor growth inhibition in all FP-RMS PDXs treated
        with single-agent FGF401 (FGFR4-specific inhibitor) and single-agent
        lenvatinib (multikinase FGFR inhibitor)
      explanation: >-
        Provides the functional precedent for testing FGFR response biomarkers
        across a broader FP-RMS model panel.
  evidence:
  - reference: PMID:42041178
    reference_title: Comprehensive Multiplatform Tyrosine Kinase Profiling Reveals Novel Actionable FGFR Aberrations across Sarcomas Affecting the Young.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A major obstacle preventing further advances and clinical implementation
      is the lack of predictive response biomarkers to guide TK-targeted
      treatments.
    explanation: >-
      Explicitly identifies predictive response biomarkers as an active barrier
      to tyrosine-kinase-targeted therapy implementation.
  - reference: PMID:42041178
    reference_title: Comprehensive Multiplatform Tyrosine Kinase Profiling Reveals Novel Actionable FGFR Aberrations across Sarcomas Affecting the Young.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The unresolved question is when upregulated TK expression is associated
      with kinase activation and signaling dependence.
    explanation: >-
      Defines the specific mechanistic and biomarker gap that applies to
      FGFR4/FGF8-high fusion-positive RMS.
- discussion_id: gap_arms_tme_immunotherapy_resistance
  prompt: >-
    In fusion-positive ARMS, is immunotherapy resistance driven by a
    fusion/enhancer-imposed immune-cold chromatin state, antigen heterogeneity,
    cancer-associated fibroblast checkpoint/cytokine support, or a combined
    tumor-intrinsic and microenvironmental resistance state?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#PAX-FOXO1 Fusion Oncogene
  - pathophysiology#PAX-FOXO1 Disease Enhancer Reprogramming
  - pathophysiology#Immune-Evasive Tumor Microenvironment
  - pathophysiology#Chemotherapy Resistance and Relapse
  - pathophysiology#Aberrant Cell Proliferation
  rationale: >-
    Recent immunotherapy and tumor-microenvironment papers make the gap more
    specific than "immunotherapy has not worked." CAR-T reviews identify limited
    clinical activity and hurdles such as antigen heterogeneity and
    immunosuppressive microenvironments; tumor-immune reviews connect PAX3:FOXO1
    to reduced antigen presentation and immune infiltration; and a 2025
    fusion-positive RMS fibroblast model shows immune-checkpoint and
    cyclophosphamide-resistance effects. With the fusion/enhancer node now
    explicit, the remaining gap is whether immune resistance is encoded in the
    tumor-cell chromatin state, imposed by CAF-supported microenvironmental
    signaling, or produced by both layers together.
  proposed_experiments:
  - experiment_id: exp_arms_tme_coculture_immunotherapy_resistance_panel
    name: FP-RMS tumor-CAF-immune coculture resistance panel
    description: >-
      Build human FP-RMS tumor-cell, cancer-associated fibroblast, and immune
      cocultures with matched antigen-expression, cytokine, single-cell
      transcriptomic, and open-chromatin profiling. Test CAR-T targets,
      checkpoint blockade, CXCR4 inhibition, CAF depletion, and fusion/enhancer
      perturbation to distinguish antigen-loss, tumor-intrinsic immune-cold
      chromatin, immune-exclusion, and fibroblast-mediated resistance
      mechanisms.
    experiment_type:
      preferred_term: tumor microenvironment immunotherapy resistance experiment
    model_systems:
    - name: FP-RMS tumor-CAF-immune coculture
      description: >-
        Human fusion-positive rhabdomyosarcoma tumor cells cocultured with
        patient-derived or metastatic-site cancer-associated fibroblasts and T
        cells.
      experimental_model_type: CO_CULTURE
      organism:
        preferred_term: human
        term:
          id: NCBITaxon:9606
          label: Homo sapiens
      cell_types:
      - preferred_term: cancer-associated fibroblast
        term:
          id: CL:0000057
          label: fibroblast
      - preferred_term: T cell
        term:
          id: CL:0000084
          label: T cell
      publication: PMID:41131073
      modeled_mechanisms:
      - target: PAX-FOXO1 Disease Enhancer Reprogramming
        description: Tests whether fusion/enhancer state directly controls antigen-presentation or immune-exclusion programs.
      - target: Immune-Evasive Tumor Microenvironment
        description: Tests whether fibroblast and immune-cell context creates therapy resistance.
      - target: Chemotherapy Resistance and Relapse
        description: Tests whether TME support converges with relapse and chemotherapy-resistance states.
      - target: Aberrant Cell Proliferation
        description: Measures whether microenvironmental support sustains growth under therapy.
    perturbations:
    - name: CAR-T and checkpoint intervention
      target: pathophysiology#Immune-Evasive Tumor Microenvironment
      description: >-
        Compare single-antigen and dual-antigen CAR-T approaches with checkpoint
        blockade in the presence and absence of fibroblast-conditioned
        microenvironmental support.
    - name: CAF/CXCR4-axis disruption
      target: pathophysiology#Immune-Evasive Tumor Microenvironment
      description: >-
        Deplete fibroblasts or inhibit CXCR4-linked signaling to test whether
        CAF-derived factors drive immune evasion and chemotherapy resistance.
    - name: Fusion/enhancer-state perturbation
      target: pathophysiology#PAX-FOXO1 Disease Enhancer Reprogramming
      description: >-
        Perturb the fusion/enhancer program with fusion withdrawal or selected
        chromatin-handle interventions to test whether antigen presentation and
        T-cell killing can be restored from the tumor-cell side.
    readouts:
    - name: Antigen-presentation chromatin and immune infiltration state
      target: pathophysiology#Immune-Evasive Tumor Microenvironment
      description: >-
        Measure open chromatin and expression at antigen-presentation and
        immune-response programs, target-antigen expression, T-cell killing,
        immune-checkpoint expression, cytokines, and tumor-cell survival after
        immunotherapy challenge.
      biological_processes:
      - preferred_term: antigen processing and presentation
        term:
          id: GO:0019882
          label: antigen processing and presentation
      - preferred_term: immune response
        term:
          id: GO:0006955
          label: immune response
      assays:
      - preferred_term: ATAC-seq
      - preferred_term: single-cell RNA-seq
      - preferred_term: flow cytometry
      - preferred_term: cytokine profiling
      - preferred_term: cell killing assay
      direction: POSITIVE
    - name: Chemotherapy and immunotherapy resistance
      target: pathophysiology#Immune-Evasive Tumor Microenvironment
      description: >-
        Quantify cyclophosphamide sensitivity, CAR-T cytotoxicity, checkpoint
        response, and rescue by CAF/CXCR4-axis perturbation.
      assays:
      - preferred_term: cell viability assay
      - preferred_term: cytotoxicity assay
      direction: NEGATIVE
    controls:
    - name: Tumor-only and normal fibroblast coculture controls
      description: Separates CAF-specific effects from generic stromal support.
    - name: Antigen-negative CAR-T control
      description: Controls for nonspecific T-cell activation or cytotoxicity.
    decision_criterion: >-
      A resistance mechanism is prioritized if its perturbation restores
      antigen-presentation chromatin or expression, improves T-cell killing, and
      improves chemotherapy or immunotherapy response in CAF-supported FP-RMS
      cultures, while tumor-only, normal-fibroblast, or fusion-negative controls
      lack the same resistance phenotype.
    would_support:
    - pathophysiology#PAX-FOXO1 Disease Enhancer Reprogramming
    - pathophysiology#Immune-Evasive Tumor Microenvironment
    would_refute:
    - pathophysiology#Immune-Evasive Tumor Microenvironment
    evidence:
    - reference: PMID:41131073
      reference_title: Cancer-associated fibroblasts promote tumor progression in fusion-positive rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        This study establishes a model of cancer-associated fibroblasts from
        metastatic fusion-positive rhabdomyosarcoma.
      explanation: >-
        Supports feasibility of the proposed FP-RMS CAF coculture model system.
    - reference: PMID:41709231
      reference_title: CAR-T cell immunotherapy in rhabdomyosarcoma.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Significant clinical hurdles include antigen heterogeneity,
        immunosuppressive tumor microenvironments, and logistical barriers in
        manufacturing.
      explanation: >-
        Supports testing antigen heterogeneity and immunosuppressive TME as
        explicit resistance mechanisms for CAR-T strategies.
  evidence:
  - reference: PMID:41709231
    reference_title: CAR-T cell immunotherapy in rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      While preclinical studies are promising, antitumor activity in clinical
      studies to date has been limited.
    explanation: >-
      Establishes that immunotherapy resistance remains clinically relevant
      despite preclinical CAR-T promise.
  - reference: PMID:41007114
    reference_title: "Tumor-Immune Interactions in Pediatric Oral Rhabdomyosarcoma: A Narrative Review on Immuno-Oncology and Emerging Therapies."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      pediatric RMS typically exhibits a "cold" immune profile, characterized
      by minimal T-cell infiltration, a low mutational burden, and resistance to
      immune checkpoint blockade.
    explanation: >-
      Supports an immune-cold pediatric RMS context that may contribute to poor
      checkpoint response, while remaining broader than ARMS-only.
  - reference: PMID:41131073
    reference_title: Cancer-associated fibroblasts promote tumor progression in fusion-positive rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Altogether, our results describe tumor-promoting mechanisms of growth,
      migration, and treatment resistance supported by the tumor
      microenvironment
    explanation: >-
      Supports a direct FP-RMS microenvironmental resistance mechanism that the
      proposed experiment should dissect.
disease_term:
  preferred_term: alveolar rhabdomyosarcoma
  term:
    id: MONDO:0009994
    label: alveolar rhabdomyosarcoma

classifications:
  icdo_morphology:
    classification_value: Sarcoma
    evidence:
    - reference: PMID:10337369
      reference_title: "Rhabdomyosarcoma: an overview."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Rhabdomyosarcoma (RMS) is a malignant tumor of mesenchymal origin thought to"
      explanation: Rhabdomyosarcoma is a malignant mesenchymal tumor (sarcoma), supporting the ICD-O sarcoma morphology assignment.
  harrisons_chapter:
  - classification_value: ONCOLOGY_HEMATOLOGY
    evidence:
    - reference: PMID:10337369
      reference_title: "Rhabdomyosarcoma: an overview."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Rhabdomyosarcoma (RMS) is a malignant tumor of mesenchymal origin thought to"
      explanation: Rhabdomyosarcoma is an oncologic malignancy, supporting the Harrison's Oncology and Hematology classification.
datasets:
- accession: geo:GSE83728
  title: >-
    Histone H3K27ac ChIP-seq, PAX3-FOXO1 ChIP-seq, BRD4 ChIP-seq, DNase-seq,
    RNA-seq and 4C-seq in FP-RMS cell lines and patient-derived cultures
    (Gryder et al. 2017 Cancer Discovery SuperSeries)
  description: >-
    Foundational epigenomic atlas of the PAX3-FOXO1 super-enhancer regulatory
    program in fusion-positive ARMS. Includes H3K27ac, BRD4, MED1, MYOD, MYOG,
    MYCN, CTCF, and PAX3-FOXO1 ChIP-seq across RH3, RH4, RH5, RH41 (FP-ARMS),
    RD (ERMS), and patient-derived primary cultures (≥10 donors), plus a causal
    fibroblast model (7250 cells ± PAX3-FOXO1). DNase-seq and 4C-seq provide
    chromatin-accessibility and 3D contact data. Subseries GSE83726 contains
    H3K27ac ChIP-seq from primary human ARMS tumor biopsies. Defines the
    BET-bromodomain vulnerability of the PAX3-FOXO1 transcriptional program.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: MULTI_OMICS
  sample_types:
  - preferred_term: alveolar rhabdomyosarcoma cell line
    tissue_term:
      preferred_term: skeletal muscle tissue
      term:
        id: UBERON:0001134
        label: skeletal muscle tissue
  sample_count: 80
  conditions:
  - fusion-positive alveolar rhabdomyosarcoma (FP-ARMS)
  - embryonal rhabdomyosarcoma (FN-RMS)
  - normal fibroblast ± PAX3-FOXO1
  platform: Illumina HiSeq 2000/2500
  publication: PMID:28446439
  evidence:
  - reference: PMID:28446439
    reference_title: "PAX3-FOXO1 Establishes Myogenic Super Enhancers and Confers BET Bromodomain Vulnerability."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We find PAX3-FOXO1 reprograms the cis-regulatory landscape by inducing de novo super enhancers."
    explanation: "The dataset's companion study defines the PAX3-FOXO1 super-enhancer program that this epigenomic atlas maps."
  notes: >-
    SuperSeries; subseries GSE83724 (RNA-seq), GSE83725 (fibroblast causal
    model ChIP/DNase), GSE83726 (primary tumor H3K27ac), GSE83727 (4C-seq).
    The fibroblast subseries (GSE83725) provides the cleanest causal model for
    PAX3-FOXO1 pioneer-factor chromatin remodelling independent of pre-existing
    RMS epigenome.

- accession: geo:GSE183281
  title: >-
    dTAG-mediated PAX3-FOXO1 degradation time-course in FP-RMS:
    ATAC-seq, PRO-seq, ChIP-seq, CUT&RUN, RNA-seq (Gryder et al. 2022)
  description: >-
    Most causally informative ARMS dataset available. Uses dTAG-mediated
    targeted degradation of endogenously tagged PAX3-FOXO1 in RH4 and RH30
    cell lines with time-resolved multi-omics (0.5–72 h). ATAC-seq tracks
    chromatin accessibility loss in real time; PRO-seq captures nascent
    enhancer RNA transcription to identify active super-enhancer elements;
    CUT&RUN maps histone marks; RNA-seq defines direct vs. indirect gene
    expression responses. SuperSeries comprising 10 subseries (≥209 samples
    total). Definitively distinguishes immediate-early PAX3-FOXO1 direct
    targets from secondary transcriptional cascades.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: MULTI_OMICS_PERTURBATION
  sample_types:
  - preferred_term: alveolar rhabdomyosarcoma cell line
    tissue_term:
      preferred_term: skeletal muscle tissue
      term:
        id: UBERON:0001134
        label: skeletal muscle tissue
  sample_count: 209
  conditions:
  - PAX3-FOXO1 dTAG degradation (0.5–72 h time course)
  - DMSO control
  platform: Illumina NovaSeq 6000
  publication: PMID:36395771
  evidence:
  - reference: PMID:36395771
    reference_title: "PAX3-FOXO1 coordinates enhancer architecture, eRNA transcription, and RNA polymerase pause release at select gene targets."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We used a chemical-genetic approach to rapidly degrade a canonical transcriptional activator, PAX3-FOXO1, to define the mechanism by which it regulates gene expression programs."
    explanation: "Describes the rapid PAX3-FOXO1 degradation strategy that generated this time-resolved multi-omics dataset."
  notes: >-
    SuperSeries (GSE183281); 10 component subseries covering ATAC-seq, PRO-seq,
    ChIP-seq, CUT&RUN, and RNA-seq in RH4 and RH30 lines. The PRO-seq
    component is unique — capturing eRNA transcription at active super-enhancers
    provides the most direct readout of PAX3-FOXO1 SE activity available in
    any published ARMS dataset.

- accession: geo:GSE218974
  title: >-
    Single-cell transcriptomics of alveolar rhabdomyosarcoma identifies
    PAX3::FOXO1-maintained progenitor state (Danielli et al. 2023)
  description: >-
    scRNA-seq of patient-derived aRMS and eRMS primary cultures plus RH4/RH30
    cell lines (~53,000 cells total). Identifies a PAX3::FOXO1-stabilized
    "myogenin+ cycling progenitor" cell state that persists across individual
    tumors. PAX3::FOXO1 shRNA knockdown releases the differentiation block and
    shifts cells toward a myogenin-high differentiated state. Companion CyTOF
    mass cytometry and a 244-compound phenotypic drug screen (MYOscopy imaging)
    identify MEK inhibitor (trametinib) + RAF inhibitor (dabrafenib) as cell-
    fate hijackers that redirect aRMS toward differentiation. Survival analysis
    shows the progenitor/MuSC-like transcriptional signature correlates with
    inferior patient outcomes.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: SINGLE_CELL_RNA_SEQ
  sample_types:
  - preferred_term: alveolar rhabdomyosarcoma cell
    tissue_term:
      preferred_term: skeletal muscle tissue
      term:
        id: UBERON:0001134
        label: skeletal muscle tissue
  sample_count: 7
  conditions:
  - alveolar rhabdomyosarcoma (aRMS) patient-derived cultures
  - embryonal rhabdomyosarcoma (eRMS)
  - PAX3::FOXO1 shRNA knockdown
  platform: 10x Genomics Chromium; Illumina NovaSeq 6000
  publication: PMID:36753540
  evidence:
  - reference: PMID:36753540
    reference_title: Single-cell profiling of alveolar rhabdomyosarcoma reveals RAS pathway inhibitors as cell-fate hijackers with therapeutic relevance.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Here, we combined single-cell RNA sequencing, mass cytometry, and
      high-content imaging to resolve intratumoral heterogeneity of
      patient-derived primary RMS cultures.
    explanation: >-
      Supports the patient-derived single-cell culture dataset and its
      multimodal profiling design.
  notes: >-
    GEO series GSE218974 (7 samples, ~53,000 cells). Companion CyTOF data and
    244-compound drug screen (MYOscopy) data are not deposited to GEO but are
    described in PMID:36753540. Most ARMS-focused scRNA-seq dataset; directly
    interrogates the PAX3::FOXO1 cell-fate lock with perturbation experiments.

- accession: geo:GSE174376
  title: >-
    Single-cell and single-nucleus RNA-seq + scATAC-seq atlas of pediatric
    rhabdomyosarcoma with lineage tracking and therapy-resistant states
    (Patel et al. 2022 Dev Cell)
  description: >-
    Comprehensive single-cell atlas (122,731 nuclei/cells) from 18 primary
    patient tumors (6 ARMS + 12 ERMS), 18 orthotopic PDX models, and
    organoids. Multi-modal: snRNA-seq (frozen tumors), scRNA-seq (fresh),
    scATAC-seq (paired chromatin accessibility), and lentiviral barcode
    lineage tracking. Defines a 3-state myogenic developmental hierarchy
    (progenitor / myoblast-like / myocyte-like) shared across subtypes.
    ARMS shows a narrower late-stage developmental bias vs. ERMS. scATAC-seq
    links chromatin accessibility to cell-state transitions. Chemotherapy
    selects for ABCG2+ mesoderm-like quiescent progenitor cells, providing a
    mechanistic model for disease relapse. Includes matched pre/post-treatment
    samples from RMS13 clinical trial.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: SINGLE_CELL_RNA_SEQ
  sample_types:
  - preferred_term: rhabdomyosarcoma tumor
    tissue_term:
      preferred_term: skeletal muscle tissue
      term:
        id: UBERON:0001134
        label: skeletal muscle tissue
  sample_count: 64
  conditions:
  - alveolar rhabdomyosarcoma (ARMS)
  - embryonal rhabdomyosarcoma (ERMS)
  - treatment-naive
  - post-chemotherapy
  platform: 10x Genomics Chromium; Illumina HiSeq 4000/NovaSeq
  publication: PMID:35483358
  evidence:
  - reference: PMID:35483358
    reference_title: The myogenesis program drives clonal selection and drug resistance in rhabdomyosarcoma.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Here, we use single-cell and single-nucleus RNA sequencing to show that
      RMS tumors recapitulate the spectrum of embryonal myogenesis.
    explanation: >-
      Supports the principal single-cell and single-nucleus dataset design;
      ARMS-specific sample composition is accession metadata rather than a
      claim established by this abstract sentence.
  notes: >-
    GEO series GSE174376. Uniformly processed open-access downloads available
    via ScPCA project SCPCP000005 (Alex's Lemonade Stand Foundation) as
    SingleCellExperiment and AnnData objects. The paired scATAC-seq (6 samples)
    is the only publicly available chromatin-accessibility data from primary
    human ARMS patient tissue.

- accession: dbgap:phs000720
  title: >-
    Comprehensive genomic analysis of rhabdomyosarcoma — WGS, WES, and
    RNA-seq of primary human tumors (Shern et al. 2014 Cancer Discovery)
  description: >-
    Reference multi-platform genomic landscape study of primary human
    rhabdomyosarcoma. Includes WGS (44 tumor/normal pairs at ~105× depth),
    WES (103 tumor/normal pairs), RNA-seq (80 tumors), and SNP arrays (865
    consented subjects in dbGaP v5). PAX3-FOXO1 (n≈35) and PAX7-FOXO1
    (n≈15) fusion-positive cases dominate the cohort. Establishes that the
    RTK/RAS/PIK3CA genetic axis is altered in 93% of cases, revealing a
    framework for genomics-directed therapy. Identifies the recurrent secondary
    somatic landscape (MYCN amplification, CDK4/CDKN2A alterations, TP53
    mutations) co-occurring with PAX fusions. Publicly accessible mutation
    summary and expression data via cBioPortal study rms_nih_2014; raw
    BAM/VCF files require dbGaP controlled-access approval.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: MULTI_OMICS
  sample_types:
  - preferred_term: rhabdomyosarcoma tumor
    tissue_term:
      preferred_term: skeletal muscle tissue
      term:
        id: UBERON:0001134
        label: skeletal muscle tissue
  sample_count: 147
  conditions:
  - fusion-positive rhabdomyosarcoma (PAX3-FOXO1 and PAX7-FOXO1)
  - fusion-negative rhabdomyosarcoma
  platform: Illumina HiSeq 2000; Illumina Omni 2.5M/5M SNP arrays
  publication: PMID:24436047
  evidence:
  - reference: PMID:24436047
    reference_title: Comprehensive genomic analysis of rhabdomyosarcoma reveals a landscape of alterations affecting a common genetic axis in fusion-positive and fusion-negative tumors.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we report a collaborative effort between the National Cancer
      Institute, the Children's Oncology Group, and the Broad Institute using a
      combination of whole-genome, whole-exome and whole-transcriptome
      sequencing along with high resolution SNP arrays to characterize the
      landscape of somatic alterations in 147 tumor/normal pairs.
    explanation: >-
      Directly supports the multi-platform design, collaborators, and cohort
      size represented by this dbGaP record.
  notes: >-
    dbGaP accession phs000720 (currently v5.p2). Open summary-level mutation
    and expression data accessible via cBioPortal study rms_nih_2014
    (https://www.cbioportal.org/study/summary?id=rms_nih_2014). This is the
    same study cited in the genetic and pathophysiology sections (PMID:24436047);
    the dataset entry enables direct linkage to the raw data repository.

references:
- reference: PMID:39686893
  title: "[Characteristics of the cytogenetic variants of alveolar rhabdomyosarcoma]."
- reference: PMID:22454413
  title: PAX3/FOXO1 fusion gene status is the key prognostic molecular marker in rhabdomyosarcoma and significantly improves current risk stratification.
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: PMID:32044412
  title: Patterns of Failure in Parameningeal Alveolar Rhabdomyosarcoma.
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: PMID:41721480
  title: "Children and Young People With First Relapse or Progression of Upfront Metastatic Rhabdomyosarcoma: An Analysis of Clinical Features and Outcomes From the INternational Soft Tissue saRcoma ConsorTium (INSTRuCT)."
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: PMID:40508013
  title: "Molecular Targets in Alveolar Rhabdomyosarcoma: A Narrative Review of Progress and Pitfalls."
- reference: PMID:39448867
  title: Dependence of PAX3-FOXO1 chromatin occupancy on ETS1 at important disease-promoting genes exposes new targetable vulnerability in Fusion-Positive Rhabdomyosarcoma.
- reference: PMID:41401084
  title: Therapeutic targeting of YOD1 disrupts the PAX-FOXO1/N-Myc feedback loop in rhabdomyosarcoma.
- reference: PMID:42041178
  title: Comprehensive Multiplatform Tyrosine Kinase Profiling Reveals Novel Actionable FGFR Aberrations across Sarcomas Affecting the Young.
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: PMID:39147820
  title: Entinostat as a combinatorial therapeutic for rhabdomyosarcoma.
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: PMID:41131073
  title: Cancer-associated fibroblasts promote tumor progression in fusion-positive rhabdomyosarcoma.
- reference: PMID:24436047
  title: Comprehensive genomic analysis of rhabdomyosarcoma reveals a landscape of alterations affecting a common genetic axis in fusion-positive and fusion-negative tumors.
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: PMID:41007114
  title: "Tumor-Immune Interactions in Pediatric Oral Rhabdomyosarcoma: A Narrative Review on Immuno-Oncology and Emerging Therapies."
- reference: PMID:28058850
  title: Molecular diagnostics in the management of rhabdomyosarcoma.
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: PMID:39792629
  title: "Adult and pediatric orbital rhabdomyosarcoma: comparison of characteristics and outcomes."
- reference: DOI:10.1200/jco.22.00409
  title: "Circulating Tumor DNA Is Prognostic in Intermediate-Risk Rhabdomyosarcoma: A Report From the Children's Oncology Group"
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-falcon.md
- reference: PMID:40790568
  title: Predictors of survival among children and adolescents with rhabdomyosarcoma treated in a single resource-limited centre -Uganda.
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: PMID:41986061
  title: "Primary orbital B cell lymphoblastic lymphoma in a toddler mimicking rhabdomyosarcoma: a diagnostic challenge."
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: PMID:41828638
  title: "Gene Amplification in Rhabdomyosarcoma: Lessons from a Rare Cancer."
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: PMID:41038289
  title: Towards directed therapy for fusion-positive rhabdomyosarcoma.
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: PMID:31562043
  title: "Vinorelbine and continuous low-dose cyclophosphamide as maintenance chemotherapy in patients with high-risk rhabdomyosarcoma (RMS 2005): a multicentre, open-label, randomised, phase 3 trial."
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: PMID:30351457
  title: "The addition of cixutumumab or temozolomide to intensive multiagent chemotherapy is feasible but does not improve outcome for patients with metastatic rhabdomyosarcoma: A report from the Children's Oncology Group."
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: PMID:39809723
  title: Rhabdomyosarcoma Surgical Update.
- reference: PMID:32124549
  title: "Do children and adolescents with completely resected alveolar rhabdomyosarcoma require adjuvant radiation? A report from the Children's Oncology Group."
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: clinicaltrials:NCT02567435
  title: A Randomized Phase 3 Study of Vincristine, Dactinomycin, Cyclophosphamide (VAC) Alternating With Vincristine and Irinotecan (VI) Versus VAC/VI Plus Temsirolimus (TORI, Torisel, NSC# 683864) in Patients With Intermediate Risk (IR) Rhabdomyosarcoma (RMS)
- reference: PMID:36753540
  title: Single-cell profiling of alveolar rhabdomyosarcoma reveals RAS pathway inhibitors as cell-fate hijackers with therapeutic relevance.
- reference: PMID:41709231
  title: CAR-T cell immunotherapy in rhabdomyosarcoma.
  found_in:
  - Alveolar_Rhabdomyosarcoma-deep-research-openscientist.md
- reference: PMID:10337369
  title: "Rhabdomyosarcoma: an overview."
- reference: PMID:28446439
  title: "PAX3-FOXO1 Establishes Myogenic Super Enhancers and Confers BET Bromodomain Vulnerability."
- reference: PMID:36395771
  title: "PAX3-FOXO1 coordinates enhancer architecture, eRNA transcription, and RNA polymerase pause release at select gene targets."
- reference: PMID:35483358
  title: The myogenesis program drives clonal selection and drug resistance in rhabdomyosarcoma.
📚

References & Deep Research

References

30
PMID:39686893
[Characteristics of the cytogenetic variants of alveolar rhabdomyosarcoma].
No top-level findings curated for this source.
PMID:22454413
PAX3/FOXO1 fusion gene status is the key prognostic molecular marker in rhabdomyosarcoma and significantly improves current risk stratification.
No top-level findings curated for this source.
PMID:32044412
Patterns of Failure in Parameningeal Alveolar Rhabdomyosarcoma.
No top-level findings curated for this source.
PMID:41721480
Children and Young People With First Relapse or Progression of Upfront Metastatic Rhabdomyosarcoma: An Analysis of Clinical Features and Outcomes From the INternational Soft Tissue saRcoma ConsorTium (INSTRuCT).
No top-level findings curated for this source.
PMID:40508013
Molecular Targets in Alveolar Rhabdomyosarcoma: A Narrative Review of Progress and Pitfalls.
No top-level findings curated for this source.
PMID:39448867
Dependence of PAX3-FOXO1 chromatin occupancy on ETS1 at important disease-promoting genes exposes new targetable vulnerability in Fusion-Positive Rhabdomyosarcoma.
No top-level findings curated for this source.
PMID:41401084
Therapeutic targeting of YOD1 disrupts the PAX-FOXO1/N-Myc feedback loop in rhabdomyosarcoma.
No top-level findings curated for this source.
PMID:42041178
Comprehensive Multiplatform Tyrosine Kinase Profiling Reveals Novel Actionable FGFR Aberrations across Sarcomas Affecting the Young.
No top-level findings curated for this source.
PMID:39147820
Entinostat as a combinatorial therapeutic for rhabdomyosarcoma.
No top-level findings curated for this source.
PMID:41131073
Cancer-associated fibroblasts promote tumor progression in fusion-positive rhabdomyosarcoma.
No top-level findings curated for this source.
PMID:24436047
Comprehensive genomic analysis of rhabdomyosarcoma reveals a landscape of alterations affecting a common genetic axis in fusion-positive and fusion-negative tumors.
No top-level findings curated for this source.
PMID:41007114
Tumor-Immune Interactions in Pediatric Oral Rhabdomyosarcoma: A Narrative Review on Immuno-Oncology and Emerging Therapies.
No top-level findings curated for this source.
PMID:28058850
Molecular diagnostics in the management of rhabdomyosarcoma.
No top-level findings curated for this source.
PMID:39792629
Adult and pediatric orbital rhabdomyosarcoma: comparison of characteristics and outcomes.
No top-level findings curated for this source.
DOI:10.1200/jco.22.00409
Circulating Tumor DNA Is Prognostic in Intermediate-Risk Rhabdomyosarcoma: A Report From the Children's Oncology Group
No top-level findings curated for this source.
PMID:40790568
Predictors of survival among children and adolescents with rhabdomyosarcoma treated in a single resource-limited centre -Uganda.
No top-level findings curated for this source.
PMID:41986061
Primary orbital B cell lymphoblastic lymphoma in a toddler mimicking rhabdomyosarcoma: a diagnostic challenge.
No top-level findings curated for this source.
PMID:41828638
Gene Amplification in Rhabdomyosarcoma: Lessons from a Rare Cancer.
No top-level findings curated for this source.
PMID:41038289
Towards directed therapy for fusion-positive rhabdomyosarcoma.
No top-level findings curated for this source.
PMID:31562043
Vinorelbine and continuous low-dose cyclophosphamide as maintenance chemotherapy in patients with high-risk rhabdomyosarcoma (RMS 2005): a multicentre, open-label, randomised, phase 3 trial.
No top-level findings curated for this source.
PMID:30351457
The addition of cixutumumab or temozolomide to intensive multiagent chemotherapy is feasible but does not improve outcome for patients with metastatic rhabdomyosarcoma: A report from the Children's Oncology Group.
No top-level findings curated for this source.
PMID:39809723
Rhabdomyosarcoma Surgical Update.
No top-level findings curated for this source.
PMID:32124549
Do children and adolescents with completely resected alveolar rhabdomyosarcoma require adjuvant radiation? A report from the Children's Oncology Group.
No top-level findings curated for this source.
clinicaltrials:NCT02567435
A Randomized Phase 3 Study of Vincristine, Dactinomycin, Cyclophosphamide (VAC) Alternating With Vincristine and Irinotecan (VI) Versus VAC/VI Plus Temsirolimus (TORI, Torisel, NSC# 683864) in Patients With Intermediate Risk (IR) Rhabdomyosarcoma (RMS)
No top-level findings curated for this source.
PMID:36753540
Single-cell profiling of alveolar rhabdomyosarcoma reveals RAS pathway inhibitors as cell-fate hijackers with therapeutic relevance.
No top-level findings curated for this source.
PMID:41709231
CAR-T cell immunotherapy in rhabdomyosarcoma.
No top-level findings curated for this source.
PMID:10337369
Rhabdomyosarcoma: an overview.
No top-level findings curated for this source.
PMID:28446439
PAX3-FOXO1 Establishes Myogenic Super Enhancers and Confers BET Bromodomain Vulnerability.
No top-level findings curated for this source.
PMID:36395771
PAX3-FOXO1 coordinates enhancer architecture, eRNA transcription, and RNA polymerase pause release at select gene targets.
No top-level findings curated for this source.
PMID:35483358
The myogenesis program drives clonal selection and drug resistance in rhabdomyosarcoma.
No top-level findings curated for this source.

Deep Research

2
Falcon ▸
Disease Characteristics Research Template
Edison Scientific Literature 33 citations 2026-04-05T12:21:44.575475

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Disease Characteristics Research Template

Target Disease

  • Disease Name: Alveolar Rhabdomyosarcoma
  • MONDO ID: (if available)
  • Category:

Research Objectives

Please provide a comprehensive research report on Alveolar Rhabdomyosarcoma covering all of the disease characteristics listed below. This report will be used to populate a disease knowledge base entry. Be thorough and cite primary literature (PMID preferred) for all claims.

For each section, suggested databases/resources are listed. These are the first places you should search for information on each topic.

1. Disease Information

Search first: OMIM, Orphanet, ICD-10/ICD-11, MeSH, PubMed

  • What is the disease? Provide a concise overview.
  • What are the key identifiers? (OMIM, Orphanet, ICD-10/ICD-11, MeSH, Mondo)
  • What are the common synonyms and alternative names?
  • Is the information derived from individual patients (e.g., EHR) or aggregated disease-level resources?

2. Etiology

  • Disease Causal Factors: What are the primary causes? (genetic, environmental, infectious, mechanistic)
  • Risk Factors:

    Search first: PubMed, Cochrane Library, UpToDate, clinical guidelines, ClinVar, ClinGen, GWAS Catalog, PheGenI, CTD, CDC, WHO, epidemiological databases

  • Genetic risk factors (causal variants, susceptibility loci, modifier genes)
  • Environmental risk factors (toxins, lifestyle, occupational exposures, age, sex, family history)
  • Protective Factors:

    Search first: PubMed, Cochrane Library, clinical trial databases, GWAS Catalog, gnomAD, WHO, CDC, nutrition databases

  • Genetic protective factors (protective variants, modifier alleles)
  • Environmental protective factors (diet, lifestyle, exposures that reduce risk)
  • Gene-Environment Interactions: How do genetic and environmental factors interact to influence disease?

    Search first: CTD, PubMed, PheGenI, GxE databases

3. Phenotypes

Search first: HPO (Human Phenotype Ontology), OMIM, Orphanet, PubMed, clinicaltrials.gov, MedDRA, SNOMED CT, DECIPHER, LOINC

For each phenotype, provide: - Phenotype type: symptoms, clinical signs, physical manifestations, behavioral changes, or laboratory abnormalities

For symptoms/signs: HPO, OMIM, Orphanet, PubMed For behavioral changes: HPO, DSM, RDoC (Research Domain Criteria), PubMed For laboratory abnormalities: LOINC, SNOMED CT, LabTests Online, PubMed - Phenotype characteristics: Search first: OMIM, Orphanet, HPO, PubMed - Age of symptom onset (neonatal, childhood, adult-onset, late-onset) - Symptom severity (mild, moderate, severe, variable) - Symptom progression (stable, progressive, episodic, fluctuating) - Frequency among affected individuals (percentage or qualitative) - Quality of life impact: Effects on daily functioning and well-being (per-phenotype when possible) Search first: EQ-5D database, SF-36, WHO QOL databases, PubMed - Suggest HPO (Human Phenotype Ontology) terms for each phenotype

4. Genetic/Molecular Information

  • Causal Genes: Gene mutations or chromosomal abnormalities responsible for disease (gene symbols, OMIM IDs)

    Search first: OMIM, ClinVar, HGMD, Ensembl, NCBI Gene

  • Pathogenic Variants:
  • Affected genes (gene symbols, HGNC IDs) > Search first: OMIM, NCBI Gene, Ensembl, HGNC, UniProt, GeneCards
  • Variant classification (pathogenic, likely pathogenic, VUS per ACMG/AMP guidelines) > Search first: ClinVar, ClinGen, ACMG/AMP guidelines, VarSome
  • Variant type/class (missense, frameshift, nonsense, splice-site, structural)
  • Allele frequency in population databases > Search first: gnomAD, 1000 Genomes, ExAC, TOPMed, dbSNP
  • Somatic vs germline origin > Search first: COSMIC (somatic), ClinVar, ICGC, TCGA
  • Functional consequences (loss of function, gain of function, dominant negative)
  • Modifier Genes: Genes that modify disease severity or expression
  • Epigenetic Information: DNA methylation, histone modifications, chromatin changes affecting disease

    Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth

  • Chromosomal Abnormalities: Large-scale genetic changes (aneuploidy, translocations, inversions)

    Search first: DECIPHER, ClinVar, ECARUCA, UCSC Genome Browser

5. Environmental Information

  • Environmental Factors: Non-genetic contributing factors (toxins, radiation, pollution, occupational exposure)

    Search first: CTD (Comparative Toxicogenomics Database), TOXNET, PubMed, EPA databases

  • Lifestyle Factors: Behavioral factors (smoking, diet, exercise, alcohol consumption)

    Search first: CDC databases, WHO, PubMed, NHANES

  • Infectious Agents: If applicable, pathogens causing or triggering disease (bacteria, viruses, fungi, parasites)

    Search first: NCBI Taxonomy, ViPR, BV-BRC, MicrobeDB, GIDEON

6. Mechanism / Pathophysiology

  • Molecular Pathways: Specific signaling cascades or biochemical pathways involved (Wnt, MAPK, mTOR, PI3K-AKT, etc.)

    Search first: KEGG, Reactome, WikiPathways, PathBank, BioCyc

  • Cellular Processes: Cell-level mechanisms (apoptosis, autophagy, cell cycle dysregulation, inflammation, etc.)

    Search first: Gene Ontology (GO), Reactome, KEGG, PubMed

  • Protein Dysfunction: How protein structure or function is altered (misfolding, aggregation, loss of function, gain of function)

    Search first: UniProt, PDB (Protein Data Bank), InterPro, Pfam, AlphaFold

  • Metabolic Changes: Alterations in metabolic processes (energy metabolism, lipid metabolism, amino acid metabolism)

    Search first: KEGG, BioCyc, HMDB (Human Metabolome Database), BRENDA

  • Immune System Involvement: Role of immune response (autoimmunity, immunodeficiency, chronic inflammation)

    Search first: ImmPort, Immunome Database, IEDB, Gene Ontology

  • Tissue Damage Mechanisms: How tissues/ are injured (oxidative stress, ischemia, fibrosis, necrosis)

    Search first: PubMed, Gene Ontology, Reactome

  • Biochemical Abnormalities: Specific molecular defects (enzyme deficiencies, receptor dysfunction, ion channel defects)

    Search first: BRENDA, UniProt, KEGG, OMIM, PubMed

  • Epigenetic Changes: DNA methylation, histone modifications affecting gene expression in disease

    Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth

  • Molecular Profiling (if available):
  • Transcriptomics/gene expression changes > Search first: GEO (Gene Expression Omnibus), ArrayExpress, GTEx, Human Cell Atlas, SRA
  • Proteomics findings > Search first: PRIDE, ProteomeXchange, Human Protein Atlas, STRING, BioGRID
  • Metabolomics signatures > Search first: MetaboLights, Metabolomics Workbench, HMDB, METLIN
  • Lipidomics alterations > Search first: LIPID MAPS, SwissLipids, LipidHome, Metabolomics Workbench
  • Genomic structural features > Search first: UCSC Genome Browser, Ensembl, NCBI, dbVar, DGV
  • Advanced Technologies (if applicable):
  • Single-cell analysis findings (cell-type specific mechanisms, cellular heterogeneity) > Search first: Human Cell Atlas, Single Cell Portal, GEO, CELLxGENE
  • Spatial transcriptomics findings > Search first: GEO, Spatial Research, Vizgen, 10x Genomics data
  • Multi-omics integration results > Search first: TCGA, ICGC, cBioPortal, LinkedOmics, PubMed
  • Functional genomics screens (CRISPR, RNAi) > Search first: DepMap, GenomeRNAi, PubMed, BioGRID ORCS

For each mechanism, describe: - The causal chain from initial trigger to clinical manifestation - Which mechanisms are upstream vs downstream - What cell types and biological processes are involved - Suggest GO terms for biological processes and CL terms for cell types

7. Anatomical Structures Affected

  • Organ Level:
  • Primary organs directly affected
  • Secondary organ involvement (complications, secondary effects)
  • Body systems involved (cardiovascular, nervous, digestive, respiratory, endocrine, etc.)

    Search first: Uberon, FMA (Foundational Model of Anatomy), OMIM, HPO, ICD-11, MeSH, SNOMED CT

  • Tissue and Cell Level:
  • Specific tissue types affected (epithelial, connective, muscle, nervous)
  • Specific cell populations targeted (with Cell Ontology terms)

    Search first: Uberon, Human Protein Atlas, Cell Ontology, Human Cell Atlas, CellMarker, PanglaoDB

  • Subcellular Level:
  • Cellular compartments involved (mitochondria, nucleus, ER, lysosomes) (with GO Cellular Component terms)

    Search first: Gene Ontology (Cellular Component), UniProt, Human Protein Atlas

  • Localization:
  • Specific anatomical sites (with UBERON terms) > Search first: FMA, Uberon, NeuroNames (for brain), SNOMED CT
  • Lateralization (unilateral, bilateral, asymmetric) > Search first: HPO, clinical literature, imaging databases

8. Temporal Development

  • Onset:
  • Typical age of onset (congenital, pediatric, adult, geriatric)
  • Onset pattern (acute, subacute, chronic, insidious)

    Search first: OMIM, Orphanet, HPO, PubMed

  • Progression:
  • Disease stages (early, intermediate, advanced, end-stage) > Search first: Cancer Staging Manual (AJCC), WHO classifications, PubMed
  • Progression rate (rapid, slow, variable)
  • Disease course pattern (episodic, relapsing-remitting, progressive, stable)
  • Disease duration (self-limited, chronic lifelong)

    Search first: Disease registries, longitudinal cohort databases, natural history studies, PubMed, Orphanet, OMIM

  • Patterns:
  • Remission patterns (spontaneous, treatment-induced) > Search first: Clinical trial databases, disease registries, PubMed
  • Critical periods (time windows of vulnerability or opportunity for intervention) > Search first: PubMed, developmental biology databases, clinical guidelines

9. Inheritance and Population

  • Epidemiology:
  • Prevalence (cases per 100,000 at given time)
  • Incidence (new cases per 100,000 per year)

    Search first: Orphanet, CDC, WHO, GBD (Global Burden of Disease), national registries, SEER, disease registries

  • For Genetic Etiology:
  • Inheritance pattern (AD, AR, X-linked, mitochondrial, multifactorial, polygenic) > Search first: OMIM, Orphanet, ClinVar, GTR (Genetic Testing Registry)
  • Penetrance (complete, incomplete, age-dependent) > Search first: ClinVar, OMIM, PubMed, ClinGen
  • Expressivity (variable, consistent) > Search first: OMIM, ClinVar, PubMed
  • Genetic anticipation (increasing severity in successive generations) > Search first: OMIM, PubMed (especially for repeat expansion disorders)
  • Germline mosaicism > Search first: ClinVar, OMIM, genetic counseling literature, PubMed
  • Founder effects (population-specific mutations) > Search first: gnomAD, population genetics databases, PubMed
  • Consanguinity role > Search first: OMIM, population studies, genetic counseling resources
  • Carrier frequency > Search first: gnomAD, carrier screening databases, GeneReviews, GTR
  • Population Demographics:
  • Affected populations (ethnic or demographic groups with higher prevalence) > Search first: gnomAD, 1000 Genomes, PAGE Study, PubMed, population registries
  • Geographic distribution (endemic areas, regional variation) > Search first: WHO, CDC, GBD, Orphanet, geographic epidemiology databases
  • Geographic distribution of specific variants
  • Sex ratio (male:female) > Search first: Disease registries, OMIM, PubMed, epidemiological databases
  • Age distribution of affected individuals > Search first: CDC, disease registries, SEER, Orphanet

10. Diagnostics

  • Clinical Tests:
  • Laboratory tests (blood, urine, tissue chemistry, specific enzyme assays) > Search first: LOINC, LabTests Online, PubMed
  • Biomarkers (proteins, metabolites, genetic markers, circulating biomarkers) > Search first: FDA Biomarker List, BEST (Biomarkers, EndpointS, and other Tools), PubMed
  • Imaging studies (X-ray, CT, MRI, PET, ultrasound) > Search first: RadLex, DICOM, Radiopaedia, imaging databases
  • Functional tests (pulmonary function, cardiac stress tests) > Search first: LOINC, clinical guidelines, PubMed
  • Electrophysiology (EEG, EMG, ECG, nerve conduction studies) > Search first: LOINC, clinical neurophysiology databases, PubMed
  • Biopsy findings (histopathology, immunohistochemistry) > Search first: SNOMED CT, College of American Pathologists resources, PubMed
  • Pathology findings (microscopic examination) > Search first: SNOMED CT, Digital Pathology databases, PubMed
  • Genetic Testing:

    Search first: GTR (Genetic Testing Registry), GeneReviews, ClinGen

  • Overview of recommended genetic testing approach
  • Whole genome sequencing (WGS) utility > Search first: GTR, ClinVar, GEL (Genomics England), gnomAD
  • Whole exome sequencing (WES) utility > Search first: GTR, ClinVar, OMIM, GeneMatcher
  • Gene panels (which panels, which genes) > Search first: GTR, ClinVar, laboratory-specific databases
  • Single gene testing > Search first: GTR, ClinVar, OMIM, GeneReviews
  • Chromosomal microarray (CMA) > Search first: DECIPHER, ClinVar, dbVar, ECARUCA
  • Karyotyping > Search first: Chromosome Abnormality Database, ClinVar, cytogenetics resources
  • FISH > Search first: ClinVar, cytogenetics databases, PubMed
  • Mitochondrial DNA testing > Search first: MITOMAP, MSeqDR, ClinVar, GTR
  • Repeat expansion testing > Search first: GTR, ClinVar, repeat expansion databases, PubMed
  • Omics-Based Diagnostics (if applicable):
  • RNA sequencing / transcriptomics > Search first: GEO, ArrayExpress, GTEx, RNA-seq databases
  • Proteomics > Search first: PRIDE, ProteomeXchange, FDA Biomarker database
  • Metabolomics > Search first: MetaboLights, Metabolomics Workbench, HMDB
  • Epigenomics > Search first: GEO, ENCODE, Roadmap Epigenomics, MethBase
  • Liquid biopsy > Search first: COSMIC, ClinVar, liquid biopsy databases, PubMed
  • Clinical Criteria:
  • Standardized diagnostic criteria (DSM, ICD, society guidelines) > Search first: DSM-5, ICD-11, clinical society guidelines, UpToDate
  • Differential diagnosis (other conditions to rule out, with distinguishing features) > Search first: DynaMed, UpToDate, clinical decision support systems
  • Screening:
  • Screening methods for asymptomatic individuals (newborn screening, carrier screening, cascade screening) > Search first: ACMG recommendations, CDC newborn screening, GTR

11. Outcome/Prognosis

  • Survival and Mortality:
  • Survival rate (5-year, 10-year, overall) > Search first: SEER, cancer registries, disease-specific registries, PubMed
  • Life expectancy (with and without treatment if applicable) > Search first: Orphanet, disease registries, actuarial databases, PubMed
  • Mortality rate > Search first: CDC, WHO, GBD, national mortality databases
  • Disease-specific mortality (deaths directly attributable to disease) > Search first: Disease registries, CDC Wonder, GBD, PubMed
  • Morbidity and Function:
  • Morbidity (disease-related disability and health impacts) > Search first: GBD, WHO, disability databases, PubMed
  • Disability outcomes (long-term functional impairments) > Search first: ICF (International Classification of Functioning), disability registries
  • Quality of life measures (EQ-5D, SF-36, PROMIS, disease-specific tools) > Search first: EQ-5D database, SF-36, PROMIS, PubMed
  • Disease Course:
  • Complications (secondary problems: infections, organ failure, etc.) > Search first: ICD codes, disease registries, clinical databases, PubMed
  • Recovery potential (likelihood and extent of recovery, with vs without treatment) > Search first: Natural history studies, rehabilitation databases, PubMed
  • Prediction:
  • Prognostic factors (age, disease severity, biomarkers, treatment response) > Search first: Prognostic models databases, clinical calculators, PubMed
  • Prognostic biomarkers (molecular markers predicting disease course) > Search first: FDA Biomarker database, PubMed, cancer prognostic databases

12. Treatment

  • Pharmacotherapy:
  • Pharmacological treatments (drug names, drug classes, mechanisms of action) > Search first: DrugBank, RxNorm, ATC classification, DailyMed, FDA databases
  • Pharmacogenomics (how genetic variants affect drug metabolism, efficacy, toxicity) > Search first: PharmGKB, CPIC (Clinical Pharmacogenetics), FDA Table of PGx Biomarkers
  • Advanced Therapeutics:
  • Gene therapy (viral vectors, CRISPR, gene replacement, gene editing) > Search first: ClinicalTrials.gov, FDA gene therapy database, ASGCT resources
  • Cell therapy (stem cell transplant, CAR-T, cellular therapeutics) > Search first: ClinicalTrials.gov, FDA cell therapy database, FACT standards
  • RNA-based therapies (ASOs, siRNA, mRNA therapies) > Search first: ClinicalTrials.gov, FDA approvals, PubMed
  • Targeted therapies (treatments directed at specific molecular targets) > Search first: My Cancer Genome, OncoKB, ClinicalTrials.gov, FDA approvals
  • Immunotherapies (checkpoint inhibitors, monoclonal antibodies) > Search first: Cancer Immunotherapy Database, FDA approvals, ClinicalTrials.gov
  • Surgical and Interventional:
  • Surgical interventions (types of surgery, timing, outcomes) > Search first: CPT codes, surgical registries, clinical guidelines, PubMed
  • Supportive and Rehabilitative:
  • Supportive care (symptom management, pain control, nutrition) > Search first: Clinical guidelines, Cochrane Library, PubMed
  • Rehabilitation (physical therapy, occupational therapy, speech therapy) > Search first: Rehabilitation medicine databases, clinical guidelines, PubMed
  • Experimental:
  • Experimental treatments in clinical trials (with NCT identifiers if available) > Search first: ClinicalTrials.gov, EU Clinical Trials Register, WHO ICTRP
  • Treatment Outcomes:
  • Treatment response rates > Search first: Clinical trial databases, FDA reviews, systematic reviews, PubMed
  • Side effects and adverse events > Search first: FDA Adverse Event Reporting System (FAERS), MedWatch, PubMed
  • Treatment Strategy:
  • Treatment algorithms (clinical pathways, decision trees) > Search first: Clinical practice guidelines, NCCN Guidelines, UpToDate
  • Combination therapies > Search first: ClinicalTrials.gov, treatment guidelines, PubMed
  • Personalized medicine approaches (genotype-guided treatment) > Search first: My Cancer Genome, CIViC, PharmGKB, precision medicine databases

For each treatment, suggest MAXO (Medical Action Ontology) terms where applicable.

13. Prevention

  • Prevention Levels:
  • Primary prevention (preventing disease occurrence: vaccination, risk factor modification) > Search first: CDC, WHO, USPSTF recommendations, Cochrane Library
  • Secondary prevention (early detection and treatment: screening programs, early intervention) > Search first: USPSTF, CDC screening guidelines, WHO
  • Tertiary prevention (preventing complications in those with disease) > Search first: Clinical guidelines, disease management protocols, PubMed
  • Immunization: Vaccine strategies (if applicable)

    Search first: CDC vaccine schedules, WHO immunization, FDA vaccine database

  • Screening and Early Detection:
  • Screening programs (population-based: newborn screening, cancer screening) > Search first: CDC screening programs, USPSTF, cancer screening databases
  • Genetic screening (carrier screening, preimplantation genetic diagnosis, prenatal testing) > Search first: ACMG recommendations, ACOG guidelines, GTR
  • Risk stratification (identifying high-risk individuals for targeted prevention) > Search first: Risk prediction models, clinical calculators, PubMed
  • Behavioral Interventions: Lifestyle modifications to reduce risk

    Search first: CDC, WHO, behavioral intervention databases, Cochrane Library

  • Counseling: Genetic counseling (risk assessment, family planning guidance)

    Search first: NSGC resources, ACMG guidelines, GeneReviews

  • Public Health:
  • Public health interventions (sanitation, vector control, health education) > Search first: CDC, WHO, public health databases, PubMed
  • Environmental interventions (reducing environmental risk factors) > Search first: EPA databases, WHO environmental health, PubMed
  • Prophylaxis: Preventive medications or procedures

    Search first: Clinical guidelines, FDA approvals, PubMed

14. Other Species / Natural Disease

  • Taxonomy: Species affected (with NCBI Taxon identifiers)

    Search first: NCBI Taxonomy

  • Breed: Specific breeds affected (with VBO identifiers if applicable)

    Search first: VBO (Vertebrate Breed Ontology)

  • Gene: Orthologous genes in other species (with NCBI Gene IDs)

    Search first: NCBI Gene

  • Natural Disease:
  • Naturally occurring disease in other species (companion animals, wildlife) > Search first: OMIA (Online Mendelian Inheritance in Animals), VetCompass, PubMed
  • Veterinary relevance and importance in animal health > Search first: OMIA, veterinary databases, PubMed
  • Comparative Biology:
  • Comparative pathology (similarities and differences across species) > Search first: OMIA, comparative pathology databases, PubMed
  • Evolutionary conservation of disease mechanisms > Search first: HomoloGene, OrthoMCL, Alliance of Genome Resources
  • Transmission (if applicable):
  • Zoonotic potential > Search first: CDC zoonotic diseases, WHO zoonoses, GIDEON
  • Cross-species susceptibility > Search first: NCBI Taxonomy, veterinary databases, PubMed

15. Model Organisms

  • Model Types:
  • Model organism type (mammalian, invertebrate, cellular, in vitro) > Search first: Alliance of Genome Resources, model organism databases
  • Specific model systems (mouse, rat, zebrafish, Drosophila, C. elegans, yeast, cell lines, organoids, iPSCs) > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, SGD, ATCC, Cellosaurus
  • Induced models (drug treatment, surgical intervention, environmental manipulation) > Search first: MGI, model organism databases, PubMed
  • Genetic Models:
  • Types available (knockout, knock-in, transgenic, conditional, humanized) > Search first: MGI, IMPC, KOMP, EuMMCR, IMSR
  • Model Characteristics:
  • Phenotype recapitulation (how well model reproduces human disease features) > Search first: Model organism databases, comparative studies, PubMed
  • Model limitations (aspects of human disease not captured) > Search first: Model organism databases, PubMed, review articles
  • Applications:
  • Research applications (what aspects of disease can be studied) > Search first: Model organism databases, PubMed
  • Resources:
  • Model databases > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, IMSR, EMMA, MMRRC

Citation Requirements

  • Cite primary literature (PMID preferred) for all mechanistic and clinical claims
  • Prioritize recent reviews and landmark papers
  • Include direct quotes from abstracts where possible to support key statements
  • Distinguish evidence source types: human clinical, model organism, in vitro, computational

Output Format

Structure your response as a comprehensive narrative organized by the sections above. For each section, provide: - Factual content with specific details (numbers, percentages, gene names, variant nomenclature) - Ontology term suggestions (HPO, GO, CL, UBERON, CHEBI, MAXO, MONDO) where applicable - Evidence citations with PMIDs - Direct quotes from abstracts to support key claims - Clear indication when information is not available or not applicable for this disease

This report will be used to populate a disease knowledge base entry with: - Pathophysiology descriptions with causal chains - Gene/protein annotations (HGNC, GO terms) - Phenotype associations (HP terms) with frequencies - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Treatment annotations (MAXO terms) - Evidence items with PMIDs and exact abstract quotes - Epidemiology, prognosis, diagnostic, and prevention information - Animal model descriptions with phenotype recapitulation details

Disease Characteristics Research Report: Alveolar Rhabdomyosarcoma (ARMS)

Target disease

Alveolar rhabdomyosarcoma (ARMS) is an aggressive rhabdomyosarcoma (RMS) subtype (a malignant mesenchymal tumor showing skeletal muscle differentiation) that occurs primarily in children, adolescents, and young adults and is typically managed with multimodality therapy (systemic chemotherapy plus local control with surgery and/or radiotherapy). (wasti2025childhoodadolescentand pages 2-4, pantelakis2025recentadvanceson pages 1-2)

Topic Key finding Evidence type (human/model/in vitro/computational) Quantitative/statistic Citation details (first author, journal, year, PMID if present in text; otherwise DOI) URL
Liquid biopsy / prognostic biomarker Baseline ctDNA detection is feasible in intermediate-risk RMS and is prognostic; in fusion-positive RMS, detecting pathognomonic PAX3/7::FOXO1 rearrangements by Rhabdo-Seq was the best ctDNA strategy. (abbou2023circulatingtumordna pages 1-2) Human clinical cohort 124 patients total; ctDNA detected in 27/49 FP-RMS (55%); FP-RMS EFS 37% vs 70% and OS 39.2% vs 75% for ctDNA-positive vs ctDNA-negative cases. (abbou2023circulatingtumordna pages 1-2) Abbou, J Clin Oncol, 2023, DOI: 10.1200/JCO.22.00409 (abbou2023circulatingtumordna pages 1-2) https://doi.org/10.1200/JCO.22.00409
Cell of origin / developmental biology PAX3-FOXO1 can reprogram endothelial progenitors into fusion-positive RMS, supporting a non-myogenic cell of origin and showing activation of myogenic super-enhancers. (searcy2023pax3foxo1dictatesmyogenic pages 1-2, searcy2023pax3foxo1dictatesmyogenic media a3da86b9) Mouse model + human iPSC + in vivo xenograft “3-year survival rate for children with high-risk RMS has remained at 20%”; in ACP mice, 30% of 940 lineage-traced cells in SCM co-localized with PAX7; P3F-expressing TP53-null human iPSCs formed FP-RMS tumors in mice. (searcy2023pax3foxo1dictatesmyogenic pages 1-2, searcy2023pax3foxo1dictatesmyogenic media a3da86b9) Searcy, Nat Commun, 2023, DOI: 10.1038/s41467-023-43044-1 (searcy2023pax3foxo1dictatesmyogenic pages 1-2) https://doi.org/10.1038/s41467-023-43044-1
Single-cell tumor states / heterogeneity A unified single-cell atlas identified four dominant RMS cell states and showed that some FP-RMS tumors harbor tumor-acquired non-myogenic states, including a neuronal state, with implications for therapy resistance. (danielli2024singlecelltranscriptomic pages 1-2) Human tumors + PDX + primary cultures + cell lines; single-cell computational analysis 72 datasets integrated; 12 Louvain clusters collapsed into 4 dominant states: progenitor, proliferative, differentiated, and ground. (danielli2024singlecelltranscriptomic pages 1-2) Danielli, Nat Commun, 2024, DOI: 10.1038/s41467-024-50527-2 (danielli2024singlecelltranscriptomic pages 1-2) https://doi.org/10.1038/s41467-024-50527-2
Epigenetic dependency / targeted therapy Small-molecule KDM inhibitors P3FI-63/P3FI-90 suppress PAX3-FOXO1-driven transcriptional output; KDM3B emerged as the strongest biochemical target, and P3FI-90 showed in vivo antitumor activity. (kim2024kdm3binhibitorsdisrupt pages 1-2, kim2024kdm3binhibitorsdisrupt pages 10-12, kim2024kdm3binhibitorsdisrupt pages 2-3) In vitro screen + biochemical assays + xenograft models + omics 62,643-compound screen; P3FI-63 KDM3B IC50 = 7 µM; metastatic IV xenograft progression delayed (p=0.0016); orthotopic intramuscular model tumor-volume reduction (p=0.0046). (kim2024kdm3binhibitorsdisrupt pages 1-2, kim2024kdm3binhibitorsdisrupt pages 10-12, kim2024kdm3binhibitorsdisrupt pages 2-3) Kim, Nat Commun, 2024, DOI: 10.1038/s41467-024-45902-y (kim2024kdm3binhibitorsdisrupt pages 1-2, kim2024kdm3binhibitorsdisrupt pages 10-12, kim2024kdm3binhibitorsdisrupt pages 2-3) https://doi.org/10.1038/s41467-024-45902-y
Fusion diagnostics / molecular pathology One-step RT-PCR on FFPE tissue is a reliable, low-cost method for fusion detection in soft tissue tumors, with high PAX3–FOXO1 detection in ARMS and concordance with FISH. (song2023detectionofvarious pages 1-2) Human diagnostic cohort / molecular pathology 242 cases tested, 213 evaluable; overall fusion-positive rate 60% (133/213); PAX3–FOXO1 detected in 31/35 ARMS (88.6%); FISH concordant in 18/18 tested cases. (song2023detectionofvarious pages 1-2) Song, Front Cell Dev Biol, 2023, DOI: 10.3389/fcell.2023.1214262 (song2023detectionofvarious pages 1-2) https://doi.org/10.3389/fcell.2023.1214262
Fusion status and clinical aggressiveness In RMS, PAX3–FOXO1 positivity correlated with lymph node metastasis, distant metastasis, and shorter overall survival, reinforcing fusion testing as clinically informative. (song2023detectionofvarious pages 1-2) Human clinicopathologic correlation study PAX3–FOXO1 status correlated with lymph node metastasis and distant metastasis; positive patients had significantly shorter OS than fusion-negative patients. (song2023detectionofvarious pages 1-2) Song, Front Cell Dev Biol, 2023, DOI: 10.3389/fcell.2023.1214262 (song2023detectionofvarious pages 1-2) https://doi.org/10.3389/fcell.2023.1214262

Table: This table summarizes major 2023–2024 advances in alveolar/fusion-positive rhabdomyosarcoma across diagnostics, biology, prognosis, and therapeutic targeting. It is designed for rapid knowledge-base curation with quantitative findings, evidence type, and source links.

1. Disease information

1.1 Concise overview

RMS is “a mesenchymal tumour showing skeletal muscle differentiation,” and ARMS is one of the major WHO-recognized RMS histologic subtypes. (wasti2025childhoodadolescentand pages 2-4, sankhe2025fusiononcogenesin pages 1-2)

A current clinical–biologic framing is that RMS comprises two dominant molecular groups: fusion-positive (FP) tumors (most often driven by PAX3(7)::FOXO1 fusions and classically associated with alveolar histology) and fusion-negative (FN) tumors (more often embryonal histology and molecularly heterogeneous). (wasti2025childhoodadolescentand pages 2-4)

1.2 Synonyms / alternative names

Commonly used synonyms and near-synonyms in the literature include: - “Alveolar RMS / aRMS” (histology-based) - “Fusion-positive RMS / FP-RMS” (molecularly defined subset; largely overlaps classical ARMS) (wasti2025childhoodadolescentand pages 2-4, sankhe2025fusiononcogenesin pages 1-2)

1.3 Key identifiers (knowledge-base note)

In the retrieved corpus, standardized identifiers (MONDO, MeSH, ICD-10/ICD-11, Orphanet, OMIM) were not explicitly enumerated in-text; therefore, this report cannot provide a verified list from primary sources in context.

1.4 Evidence source type

Most information below is derived from aggregated disease-level resources (reviews, cooperative-group summaries, and prospective/retrospective cohorts) plus primary translational studies in cell lines, mouse models, xenografts, and patient-derived models. (wasti2025childhoodadolescentand pages 2-4, sankhe2025fusiononcogenesin pages 1-2, abbou2023circulatingtumordna pages 1-2, searcy2023pax3foxo1dictatesmyogenic pages 1-2, danielli2024singlecelltranscriptomic pages 1-2, kim2024kdm3binhibitorsdisrupt pages 1-2)

2. Etiology

2.1 Primary causal factors (genetic/mechanistic)

Pathognomonic gene fusions are central causal drivers for most ARMS/FP-RMS: - ARMS frequently harbors PAX3::FOXO1 or PAX7::FOXO1 fusions; one review cites that ~80% of ARMS harbor these fusions. (wasti2025childhoodadolescentand pages 2-4) - In a large RT-PCR fusion-detection cohort of soft tissue tumors, PAX3–FOXO1 was detected in 88.6% (31/35) of ARMS cases. (song2023detectionofvarious pages 1-2)

Direct abstract quote (mechanistic framing): Searcy et al. describe FP-RMS as “driven by the expression of the PAX3-FOXO1 (P3F) fusion oncoprotein” and emphasize that FP-RMS “occurs throughout the body in areas devoid of skeletal muscle,” motivating non-myogenic cell-of-origin models. (searcy2023pax3foxo1dictatesmyogenic pages 1-2)

2.2 Risk factors

Clinical risk/prognostic factors (often used as risk stratifiers) include fusion status, primary site, tumor size, age, extent of disease, nodal status, and metastatic status. (wasti2025childhoodadolescentand pages 1-2, wasti2025childhoodadolescentand pages 2-4)

In a pediatric single-center cohort from India (localized RMS with FOXO1 known, n=140), adverse baseline features were common (e.g., nodal disease ~39–40% and tumors >5 cm in ~56–60%), and in multivariable models, nodal involvement and very large tumor size (>10 cm) were adverse prognostic factors. (ramanathan2023outcomeandprognostic pages 11-13)

Fusion status as a biologic risk factor: PAX3–FOXO1 positivity in RMS was associated with lymph node metastasis and distant metastasis in a multi-center one-step RT-PCR study, and was linked to shorter overall survival. (song2023detectionofvarious pages 1-2)

2.3 Protective factors

No protective genetic variants or environmental protective factors were identified in the retrieved sources.

2.4 Gene–environment interactions

No gene–environment interaction evidence specific to ARMS was identified in the retrieved sources.

3. Phenotypes (clinical presentation)

3.1 Typical clinical phenotype (high-level)

ARMS is a malignant soft tissue tumor that can occur in multiple anatomic sites; one case-based review notes ARMS is prevalent in adolescents and “usually develops in the extremities and can also involve the trunk, perineum, and pelvis.” (song2023detectionofvarious pages 1-2)

3.2 Phenotype characteristics (structured suggestions)

Evidence in the retrieved corpus is strongest for oncologic phenotype (local invasion, nodal/distant metastasis) rather than symptom frequency catalogs. The following HPO term suggestions are therefore provided as knowledge-base candidates (not all have frequencies in the cited sources): - Mass of soft tissue (HP:0001417) - Regional lymph node metastasis (HP:0032726) - Distant metastasis (HP:0002665) - Pain (HP:0012531) and swelling (HP:0000984) as common sarcoma presentations (not quantified in retrieved sources)

3.3 Quality of life impact

No ARMS-specific QoL instrument statistics were identified in the retrieved sources.

4. Genetic / molecular information

4.1 Causal genes / chromosomal abnormalities

Core causal alterations (somatic): - PAX3::FOXO1 and PAX7::FOXO1 fusions define FP-RMS/ARMS biology and are key diagnostic and prognostic markers. (wasti2025childhoodadolescentand pages 2-4)

Other poor-risk variants (contextual): Cooperative-group summaries note additional poor-risk variants such as MYOD1 and TP53 in RMS risk stratification discussions. (wasti2025childhoodadolescentand pages 1-2)

4.2 Variant type/class and origin

  • The canonical ARMS alterations are structural rearrangements (chromosomal translocations) yielding fusion transcription factors. (obeidin2023what’snewin pages 2-3, obeidin2023what’snewin pages 1-2)
  • These are generally somatic drivers (germline predisposition was not specifically established for ARMS in the retrieved sources).

4.3 Epigenetic dependencies and regulators (mechanistic genetics)

Recent mechanistic work underscores epigenetic and transcriptional dependencies in FP-RMS: - Searcy et al. report that PAX3-FOXO1 “functions as a pioneer transcription factor” and “activates myogenic super-enhancers that define RMS cell identity including MYOD1, MYOGENIN and MYCN.” (searcy2023pax3foxo1dictatesmyogenic pages 1-2) - Kim et al. identify small-molecule KDM3B-selective inhibitors (P3FI-63/P3FI-90) that downregulate PAX3-FOXO1 transcriptional output and alter chromatin-associated features at PAX3-FOXO1 sites; P3FI-63 inhibits KDM3B with IC50 = 7 µM. (kim2024kdm3binhibitorsdisrupt pages 2-3)

5. Environmental information

No disease-specific environmental, lifestyle, toxin, radiation, or infectious causal factors for ARMS were identified in the retrieved sources.

6. Mechanism / pathophysiology

6.1 Causal chain (current synthesis)

1) Initiating genomic event: a PAX3/7::FOXO1 fusion forms an aberrant transcription factor in FP-RMS/ARMS. (wasti2025childhoodadolescentand pages 2-4, searcy2023pax3foxo1dictatesmyogenic pages 1-2) 2) Transcriptional reprogramming: PAX3-FOXO1 can reprogram non-myogenic progenitors; Searcy et al. demonstrate PAX3-FOXO1 “reprograms mouse and human endothelial progenitors to FP-RMS.” (searcy2023pax3foxo1dictatesmyogenic pages 1-2) 3) Epigenetic remodeling and super-enhancer activation: PAX3-FOXO1 “activates myogenic super-enhancers” and establishes RMS cell identity programs. (searcy2023pax3foxo1dictatesmyogenic pages 1-2, searcy2023pax3foxo1dictatesmyogenic media 14ad6904) 4) Cell-state heterogeneity and therapy resistance: single-cell profiling identifies dominant RMS cell states and shows FP-RMS can include tumor-acquired, non-developmental programs (e.g., a neuronal state) that may persist after therapy. (danielli2024singlecelltranscriptomic pages 1-2) 5) Clinical phenotype: aggressive local behavior and higher propensity for metastasis and poor outcomes in fusion-positive disease cohorts. (wasti2025childhoodadolescentand pages 2-4, song2023detectionofvarious pages 1-2)

6.2 2023–2024 mechanistic developments (selected)

  • Cell of origin and lineage plasticity (Nov 2023, Nature Communications): Searcy et al. generate an endothelial-driven FP-RMS model and report lineage-traced myogenic stem-cell features; for example, in their ACP model “of 940 Tom+ cells counted in the SCM … 30% co-localized with PAX7.” (searcy2023pax3foxo1dictatesmyogenic pages 1-2, searcy2023pax3foxo1dictatesmyogenic media a3da86b9)
  • Single-cell atlas of RMS (Jul 2024, Nature Communications): Danielli et al. integrate 72 datasets and identify four dominant muscle-lineage cell states (progenitor, proliferative, differentiated, ground), with some FP-RMS tumors containing tumor-acquired neuronal cell states not observed in normal myogenesis. (danielli2024singlecelltranscriptomic pages 1-2)
  • Epigenetic drug discovery (Feb 2024, Nature Communications): Kim et al. screen 62,643 compounds and develop KDM3B-selective inhibitors that suppress FP-RMS growth in vivo; e.g., P3FI-90 delayed tumor progression in a metastatic IV xenograft model (p=0.0016) and reduced tumor volume in an orthotopic intramuscular model (p=0.0046). (kim2024kdm3binhibitorsdisrupt pages 1-2, kim2024kdm3binhibitorsdisrupt pages 10-12)

6.3 Suggested ontology terms (mechanisms)

GO biological process (suggestions): - Regulation of transcription by RNA polymerase II (GO:0006357) - Chromatin organization (GO:0006325) - Skeletal muscle cell differentiation (GO:0035914) - Cell cycle process (GO:0022402) - Apoptotic process (GO:0006915)

Cell types (CL suggestions): - Endothelial cell (CL:0000115) (supported conceptually by endothelial progenitor reprogramming) (searcy2023pax3foxo1dictatesmyogenic pages 1-2) - Myoblast / skeletal muscle precursor (e.g., CL:0000056 myoblast)

7. Anatomical structures affected

7.1 Organ/tissue level

ARMS is a soft tissue sarcoma that frequently arises in skeletal muscle-associated soft tissues but can occur at sites without skeletal muscle, consistent with reprogramming models and broad anatomic distribution. (searcy2023pax3foxo1dictatesmyogenic pages 1-2)

Common sites in cited literature: extremities, trunk, perineum/pelvis. (song2023detectionofvarious pages 1-2)

7.2 UBERON suggestions

  • Skeletal muscle tissue (UBERON:0001134)
  • Pelvis (UBERON:0001270)
  • Lymph node (UBERON:0000029)

8. Temporal development

8.1 Onset

RMS is predominantly pediatric/adolescent; ARMS is noted as prevalent in adolescents in clinical literature. (song2023detectionofvarious pages 1-2)

8.2 Progression

High-risk biology is linked to fusion-positive status, nodal involvement, and metastatic presentation; relapses commonly occur within ~2 years in one cohort (median relapse ~18 months). (ramanathan2023outcomeandprognostic pages 4-7)

9. Inheritance and population

9.1 Epidemiology (disease burden)

RMS accounts for ~3% of childhood cancers, with ~400–500 cases diagnosed annually in the United States (all RMS). (sankhe2025fusiononcogenesin pages 1-2)

9.2 Demographics (selected)

In a localized RMS cohort with FOXO1 status known (n=140), the median age was 4.4 years and the sex ratio was ~2.1:1 (boys:girls). (ramanathan2023outcomeandprognostic pages 2-4)

9.3 Fusion prevalence in clinical cohorts

  • Cooperative-group synthesis: ~80% of ARMS harbor PAX3/7::FOXO1 fusions. (wasti2025childhoodadolescentand pages 2-4)
  • Single-center cohort (localized RMS with fusion known): among ARMS, 25/49 (51%) were FOXO1 fusion-positive (PAX3–FOXO1 or PAX7–FOXO1). (ramanathan2023outcomeandprognostic pages 4-7)
  • Multi-center diagnostic RT-PCR cohort: PAX3–FOXO1 in 31/35 ARMS (88.6%). (song2023detectionofvarious pages 1-2)

(These differences likely reflect case mix, assay targets, and classification differences across cohorts; the retrieved sources did not provide a harmonized prevalence estimate.)

10. Diagnostics

10.1 Histopathology and immunohistochemistry (IHC)

Molecular testing is frequently needed in soft tissue tumor diagnosis; a 2023 guideline-style review emphasizes that in rhabdomyoblastic tumors molecular confirmation can be important to distinguish embryonal from alveolar RMS when morphology/IHC are insufficient, with FOXO1 fusions serving as definitive classification markers. (obeidin2023what’snewin pages 2-3)

10.2 Molecular testing approaches (2023 best-practice themes)

A morphology-driven, tiered diagnostic strategy is recommended across sarcoma molecular-testing guidance: - FISH remains useful, including break-apart probes when a fusion partner is unknown; - RT-PCR can detect known fusion breakpoints but “generally lacks the ability to detect new fusion partners”; - RNA-based NGS (hybrid-capture or anchored multiplex PCR) is increasingly adopted for sensitive fusion detection and novel partner discovery; methylation profiling is emerging for classification. (obeidin2023what’snewin pages 1-2)

10.3 ARMS-specific fusion testing performance data

Song et al. provide real-world performance data in FFPE tissues: - Among evaluable samples (n=213), overall fusion-positive rate 60% (133/213). - In ARMS, PAX3–FOXO1 detected in 88.6% (31/35). - FISH concordant with one-step RT-PCR in 18/18 tested cases. These findings support one-step RT-PCR as an accurate, low-cost fusion assay in routine settings. (song2023detectionofvarious pages 1-2)

10.4 Liquid biopsy (2023 clinical implementation direction)

Abbou et al. (COG biorepository; intermediate-risk RMS) show that baseline ctDNA is detectable and prognostic: - In FP-RMS, translocation-based ctDNA detection identified ctDNA in 27/49 (55%). - Outcomes were worse with baseline ctDNA detection (FP-RMS OS 39.2% vs 75%; EFS 37% vs 70% for ctDNA-positive vs negative). (abbou2023circulatingtumordna pages 1-2)

Direct abstract quote (purpose and conclusion excerpts): The study states, “We sought to evaluate strategies for identifying circulating tumor DNA (ctDNA) in IR RMS and to determine whether ctDNA detection before therapy is associated with outcome,” and concludes that “baseline ctDNA detection is feasible and is prognostic in IR RMS.” (abbou2023circulatingtumordna pages 1-2)

10.5 Differential diagnosis (high-level)

ARMS frequently falls within the “small round blue cell tumor” differential; the retrieved sources emphasize molecular testing (FISH/RT-PCR/NGS) to resolve histologic overlap across entities. (obeidin2023what’snewin pages 1-2, choi2023therecentadvances pages 1-2)

11. Outcome / prognosis

11.1 Survival statistics (selected)

  • In a cooperative-group synthesis, fusion-positive tumors with locoregional nodal involvement (N1) are a recognized poor-risk group; cited 5-year OS 45.5% and 5-year EFS 43%. (wasti2025childhoodadolescentand pages 2-4)
  • A broad RMS epidemiology review reports risk-group survival ranges (all RMS): low-risk ~70–90%, intermediate 50–70%, high-risk 20–30%, and highlights worse outcomes in fusion-positive disease. (pantelakis2025recentadvanceson pages 1-2)

11.2 Prognostic factors (reproducible across cohorts)

Prognosis is strongly influenced by fusion status plus classic clinicopathologic factors including tumor site, size, nodal status, metastatic status, extent of resection/residual disease, and age. (wasti2025childhoodadolescentand pages 1-2, wasti2025childhoodadolescentand pages 2-4)

11.3 Recent prognostic biomarker: ctDNA

Baseline ctDNA detection adds prognostic resolution within intermediate-risk RMS, with large differences in OS/EFS by ctDNA status as reported above. (abbou2023circulatingtumordna pages 1-2)

12. Treatment

12.1 Standard of care (real-world implementation)

Standard RMS care remains multimodality: systemic multi-agent chemotherapy combined with surgery and/or radiotherapy for local control, delivered through risk-stratified cooperative-group protocols. (wasti2025childhoodadolescentand pages 2-4, pantelakis2025recentadvanceson pages 1-2)

12.2 Risk stratification increasingly incorporates fusion status

Fusion status is emphasized as a key prognostic biomarker used alongside clinical features to guide therapy intensity and duration; algorithms are evolving as molecular biology and genomics advance. (wasti2025childhoodadolescentand pages 1-2, wasti2025childhoodadolescentand pages 2-4)

12.3 Selected clinical trials (with real-world identifiers)

Relapsed/refractory RMS (includes ARMS): - NCT01222715 (start 2010; completed 2015): randomized phase II trial of vinorelbine + cyclophosphamide combined with either bevacizumab or temsirolimus; cycles every 21 days up to 12 courses; primary objectives included feasibility and estimation/comparison of EFS. (NCT01222715 chunk 1) - NCT03041701 (start 2017; terminated): open-label phase I/II of ganitumab (anti–IGF-1R) plus dasatinib (SFK inhibitor) in relapsed/refractory embryonal or alveolar RMS; terminated due to drug availability; phase II closed early. (NCT03041701 chunk 1) - NCT02867592 (start 2017; active-not-recruiting): phase II single-group cabozantinib (oral, continuous dosing) in children/young adults with refractory/recurrent solid tumors including rhabdomyosarcoma; primary endpoint objective response rate by RECIST v1.1 for non-osteosarcoma strata. (NCT02867592 chunk 1)

High-risk RMS upfront strategy refinement: - NCT04994132 / ARST2031 (start 2021; active-not-recruiting; estimated primary completion 2026): phase III comparing VINO-AC vs VAC induction approaches, followed by vinorelbine + oral cyclophosphamide maintenance for 24 weeks; includes correlative ctDNA and genomic prognostic objectives. (NCT04994132 chunk 1)

12.4 MAXO (Medical Action Ontology) suggestions

  • Chemotherapy (MAXO:0000058)
  • Surgical resection (MAXO:0000011)
  • Radiotherapy (MAXO:0000014)
  • Molecular genetic testing (MAXO:0001001)
  • Liquid biopsy / ctDNA testing (MAXO suggestion; not validated in retrieved sources)

13. Prevention

No primary prevention strategies specific to ARMS were identified in the retrieved sources. Given the dominant role of somatic fusion oncogenes and the rarity of the disease, prevention focuses pragmatically on early diagnosis, referral to sarcoma centers, and enrollment in cooperative-group protocols (not quantitatively evaluated in retrieved sources).

14. Other species / natural disease

No naturally occurring ARMS analogs in non-human species were identified in the retrieved sources.

15. Model organisms and experimental models

Recent studies emphasize diverse model systems: - Genetically engineered mouse models and lineage tracing: Searcy et al. develop an endothelial-driven PAX3-FOXO1 model and demonstrate reprogramming toward myogenic stem-like states and FP-RMS formation. (searcy2023pax3foxo1dictatesmyogenic pages 1-2, searcy2023pax3foxo1dictatesmyogenic media a3da86b9) - Human iPSC-based developmental models: PAX3-FOXO1 expression in TP53-null iPSCs redirects differentiation and yields FP-RMS tumors in immunocompromised mice. (searcy2023pax3foxo1dictatesmyogenic pages 1-2) - Patient-derived xenografts and single-cell atlases: Danielli et al. include patient tumors, PDXs, primary cultures, and cell lines in a unified single-cell analysis, enabling cross-model comparisons of cell states and therapy-associated changes. (danielli2024singlecelltranscriptomic pages 1-2)

Limitations noted implicitly by these approaches include model dependence on engineered genetic contexts (e.g., TP53-null backgrounds), and the challenge of faithfully capturing therapy-induced and tumor-acquired states in vitro.

Expert synthesis / analysis (authoritative perspectives)

Across cooperative-group summaries, fusion status is consistently treated as a cornerstone biomarker that should be integrated into diagnostics and risk stratification, because it captures biology linked to adverse outcome and can refine treatment intensity. (wasti2025childhoodadolescentand pages 1-2, wasti2025childhoodadolescentand pages 2-4)

The 2023–2024 translational literature increasingly converges on the idea that FP-RMS is a transcriptionally and epigenetically addicted fusion-driven cancer, where vulnerabilities may lie in chromatin regulators (e.g., KDM dependencies) and in measurable tumor burden via ctDNA, rather than in high mutational burden targets. This framing is supported by direct functional studies (KDM3B inhibitors), developmental reprogramming models (endothelial progenitor origin), and clinical biomarker work (ctDNA prognostic value). (abbou2023circulatingtumordna pages 1-2, searcy2023pax3foxo1dictatesmyogenic pages 1-2, kim2024kdm3binhibitorsdisrupt pages 10-12)

References (URLs and publication dates)

  • Abbou S. et al. Journal of Clinical Oncology (May 2023). “Circulating Tumor DNA Is Prognostic in Intermediate-Risk Rhabdomyosarcoma: A Report From the Children’s Oncology Group.” https://doi.org/10.1200/jco.22.00409 (abbou2023circulatingtumordna pages 1-2)
  • Song L. et al. Frontiers in Cell and Developmental Biology (Aug 2023). “Detection of various fusion genes by one-step RT-PCR…” https://doi.org/10.3389/fcell.2023.1214262 (song2023detectionofvarious pages 1-2)
  • Searcy M.B. et al. Nature Communications (Nov 2023). “PAX3-FOXO1 dictates myogenic reprogramming…” https://doi.org/10.1038/s41467-023-43044-1 (searcy2023pax3foxo1dictatesmyogenic pages 1-2)
  • Kim Y.Y. et al. Nature Communications (Feb 2024). “KDM3B inhibitors disrupt the oncogenic activity of PAX3-FOXO1…” https://doi.org/10.1038/s41467-024-45902-y (kim2024kdm3binhibitorsdisrupt pages 1-2)
  • Danielli S.G. et al. Nature Communications (Jul 2024). “Single cell transcriptomic profiling identifies…” https://doi.org/10.1038/s41467-024-50527-2 (danielli2024singlecelltranscriptomic pages 1-2)
  • Obeidin F. Journal of Pathology and Translational Medicine (May 2023). “What’s new in bone and soft tissue pathology 2023: guidelines for molecular testing.” https://doi.org/10.4132/jptm.2023.03.20 (obeidin2023what’snewin pages 1-2)
  • ClinicalTrials.gov: NCT01222715 (2010 record; completed 2015). https://clinicaltrials.gov/study/NCT01222715 (NCT01222715 chunk 1)
  • ClinicalTrials.gov: NCT03041701 (2017 record; terminated). https://clinicaltrials.gov/study/NCT03041701 (NCT03041701 chunk 1)
  • ClinicalTrials.gov: NCT02867592 (2017 record; active-not-recruiting). https://clinicaltrials.gov/study/NCT02867592 (NCT02867592 chunk 1)
  • ClinicalTrials.gov: NCT04994132 (2021 record; active-not-recruiting). https://clinicaltrials.gov/study/NCT04994132 (NCT04994132 chunk 1)

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OpenScientist ▸
1. Disease Information
openscientist-autonomous 45 citations 2026-05-05T03:55:04.979978

1. Disease Information

Overview

Alveolar rhabdomyosarcoma (ARMS) is a high-grade malignant neoplasm of skeletal muscle lineage. It belongs to the broader family of rhabdomyosarcomas, which are the most common soft tissue sarcomas in children and adolescents. ARMS accounts for approximately 20–25% of all RMS cases, with the remainder primarily comprising embryonal rhabdomyosarcoma (ERMS). The name "alveolar" derives from its microscopic resemblance to lung alveoli, with clusters of small round blue cells separated by fibrovascular septa.

Key Identifiers

Database Identifier
MONDO MONDO:0009994
OMIM 268220
Orphanet ORPHA:99756
ICD-10 C49 (Malignant neoplasm of other connective and soft tissue), with morphology code M8920/3
ICD-11 2B5D (Rhabdomyosarcoma)
MeSH D018232 (Rhabdomyosarcoma, Alveolar)
ICD-O-3 Morphology 8920/3

Synonyms and Alternative Names

  • Alveolar RMS (ARMS)
  • Fusion-positive rhabdomyosarcoma (FP-RMS) — when harboring PAX3/7-FOXO1 fusions
  • RMA (Rhabdomyosarcoma, alveolar type)
  • PAX-FOXO1 fusion-positive rhabdomyosarcoma

Information Source

This report synthesizes information from aggregated disease-level resources including OMIM, Orphanet, SEER databases, Children's Oncology Group (COG) clinical trials, European paediatric Soft tissue sarcoma Study Group (EpSSG) trials, and primary literature from PubMed.

2. Etiology

Disease Causal Factors

ARMS is fundamentally a genetic/molecular disease driven by somatic chromosomal translocations. The primary causal events are:

  1. t(2;13)(q35;q14) — producing the PAX3-FOXO1 fusion gene (~60% of ARMS)
  2. t(1;13)(p36;q14) — producing the PAX7-FOXO1 fusion gene (~20% of ARMS)

These translocations fuse the DNA-binding domains of PAX3 or PAX7 (paired box transcription factors critical for myogenesis) with the potent transactivation domain of FOXO1 (a forkhead family transcription factor). The resultant chimeric proteins are constitutively active transcription factors that drive oncogenesis by activating proliferative programs while simultaneously blocking terminal myogenic differentiation (PMID: 10534762).

Comprehensive genomic analysis of 147 tumor/normal pairs demonstrated that: "Two genotypes are evident in rhabdomyosarcoma tumors: those characterized by the PAX3 or PAX7 fusion and those that lack these fusions but harbor mutations in key signaling pathways. The overall burden of somatic mutations in rhabdomyosarcoma is relatively low, especially in tumors that harbor a PAX3/7 gene fusion" (PMID: 24436047).

Risk Factors

Genetic Risk Factors

  • Li-Fraumeni syndrome (TP53 germline mutations): A retrospective French cohort of 31 patients with Li-Fraumeni-associated RMS found a median age at diagnosis of 2.3 years, with anaplasia reported in 12/16 reviewed cases. The 10-year cumulative risk of second malignancies was 40%, strongly influencing long-term prognosis (PMID: 32658383).
  • Beckwith-Wiedemann syndrome (11p15.5 abnormalities, IGF2 overexpression)
  • Neurofibromatosis type 1 (NF1 mutations)
  • Costello syndrome (HRAS mutations)
  • Noonan syndrome (RAS-MAPK pathway mutations)
  • DICER1 syndrome: Xeroderma pigmentosum group C patients with somatic DICER1 mutations have been reported to develop early-onset gynecological rhabdomyosarcomas (PMID: 37567969).
  • Germline predisposition to genitourinary RMS has been documented across multiple genetic syndromes (PMID: 33209717).

Environmental Risk Factors

  • Parental drug use (particularly cocaine and marijuana use during pregnancy — limited evidence)
  • Prenatal X-ray exposure (historical association, limited modern data)
  • Age: Peak incidence in childhood (ages 1–9), with a smaller peak in adolescence
  • Sex: Slight male predominance in overall RMS
  • No strong occupational or dietary environmental risk factors have been definitively established for ARMS

Protective Factors

No well-established genetic or environmental protective factors have been identified for ARMS. The rarity of the disease and its strong genetic basis (somatic translocations) limit the identification of modifiable protective factors.

Gene-Environment Interactions

Limited data exist on gene-environment interactions in ARMS. The disease appears to be predominantly driven by somatic genetic events rather than environmental exposures. However, in the context of cancer predisposition syndromes (e.g., Li-Fraumeni), the 10-year cumulative risk of second malignancies of 40% emphasizes the need to "reduce, whenever possible, the burden of genotoxic drugs and radiotherapy in carriers" (PMID: 32658383).

3. Phenotypes

Clinical Presentation

ARMS presents as a rapidly growing, often painless mass in various anatomical locations. The clinical phenotype depends on the primary tumor site.

Phenotype HPO Term Frequency Onset Severity
Soft tissue mass/swelling HP:0100774 (Neoplasm of connective tissue) >90% Childhood (peak 1–9 years) Variable
Proptosis (orbital tumors) HP:0000520 (Proptosis) ~10–15% of cases Childhood Moderate-severe
Nasal obstruction (parameningeal) HP:0001742 (Nasal obstruction) ~15–20% Childhood Moderate
Cranial nerve palsies HP:0001291 (Cranial nerve palsy) Variable (parameningeal) Childhood Severe
Hematuria (GU tumors) HP:0000790 (Hematuria) Variable Childhood Moderate
Pain at tumor site HP:0012531 (Pain) 30–50% Any Variable
Regional lymphadenopathy HP:0002716 (Lymphadenopathy) 20–40% Any Moderate
Weight loss HP:0001824 (Weight loss) Variable (advanced disease) Any Moderate-severe
Elevated serum LDH HP:0045040 (Elevated LDH) Variable At diagnosis Prognostically significant

Phenotype Characteristics

  • Age of onset: Predominantly childhood, with peak incidence between ages 1–9 years; a secondary smaller peak in adolescence (15–19 years). Median age varies by site (e.g., median 3.5 years for parameningeal ARMS, PMID: 32044412).
  • Symptom progression: Rapidly progressive; tumors typically grow over weeks to months.
  • Symptom severity: Variable, ranging from an incidental finding to life-threatening mass effect depending on anatomical location.
  • Frequency of metastatic disease at presentation: Approximately 23–27% of ARMS patients present with stage IV (metastatic) disease (PMID: 41524542; PMID: 40790568).

Quality of Life Impact

ARMS and its treatment significantly impact quality of life through: - Treatment-related toxicities (chemotherapy-induced nausea, immunosuppression, growth impairment) - Surgery-related morbidity (resection-related impairment in 33% of surviving infants, PMID: 30762282) - Long-term toxicity in 21% of survivors - Secondary malignancies in 6% of long-term survivors - Psychosocial burden on patients and families

4. Genetic/Molecular Information

Causal Genes and Chromosomal Abnormalities

Gene/Fusion Chromosome OMIM Role Frequency in ARMS
PAX3-FOXO1 t(2;13)(q35;q14) 137220 (PAX3), 136533 (FOXO1) Oncogenic fusion TF ~60%
PAX7-FOXO1 t(1;13)(p36;q14) 167410 (PAX7), 136533 (FOXO1) Oncogenic fusion TF ~20%
MYCN (amplified) 2p24 164840 Oncogene amplification Variable
CDK4 (amplified) 12q14 123829 Cell cycle regulator Variable
MDM2 (amplified) 12q15 164785 p53 inhibitor Variable

"The PAX3-FOXO1 and PAX7-FOXO1 gene fusions occur in 80% of cases with the alveolar subtype and are more predictive of outcome than histologic classification" (PMID: 28058850).

Gene amplification studies have revealed that "Studies of the pediatric soft tissue cancer alveolar rhabdomyosarcoma have contributed to the current understanding of the diverse set of molecular changes that occur as part of the gene amplification process" (PMID: 41828638).

Pathogenic Variants

  • Somatic origin: The PAX3-FOXO1 and PAX7-FOXO1 fusions are somatic events (not inherited).
  • Variant type: Chromosomal translocations producing in-frame fusion genes.
  • Functional consequence: Gain-of-function — the fusion proteins are constitutively active transcription factors with stronger transactivation than wild-type PAX3/PAX7.
  • Additional recurrent mutations (from COSMIC/TCGA): NRAS, KRAS, HRAS, FGFR4, PIK3CA, CTNNB1, FBXW7, BCOR.
  • Mutation burden: Low overall somatic mutation burden in fusion-positive tumors (PMID: 24436047).

Modifier Genes

  • TBX2: Highly upregulated in both RMS subtypes; functions as an oncogene by blocking myogenic differentiation and promoting proliferation. TBX2 interacts with MyoD and myogenin, recruits HDAC1, and represses p21 and p14. "Depletion or interference with TBX2 completely inhibits tumor growth in a xenograft assay, highlighting the oncogenic role of TBX2 in RMS cells" (PMID: 24470334).
  • SNAI2: Highly expressed in fusion-negative RMS; blocks myogenic differentiation by competing with MYOD at enhancers. RAS/MEK signaling modulates SNAI2 levels (PMID: 33420019).

Epigenetic Information

PAX3-FOXO1 drives oncogenesis through extensive epigenetic reprogramming: - Super enhancer activation: PAX3-FOXO1 activates super enhancers (SEs) to induce expression of core regulatory (CR) transcription factors. "In alveolar rhabdomyosarcoma, PAX3-FOXO1 activates SEs to induce the expression of other CR TFs, providing a model system for studying cancer cell addiction to CR transcription" (PMID: 31285436). - HDAC involvement: HDAC1/2/3 are co-essential isoforms that maintain core regulatory transcription; their co-inhibition halts CR transcription and disrupts chromatin looping. - DNA methylation: Aberrant methylation patterns associated with fusion-positive tumors have been used for epigenetic classification; cutaneous epithelioid/pleomorphic RMS can be distinguished from melanoma by DNA methylation profiling (PMID: 41780801).

Chromosomal Abnormalities

  • t(2;13)(q35;q14): PAX3-FOXO1 fusion (most common)
  • t(1;13)(p36;q14): PAX7-FOXO1 fusion (variant translocation)
  • Gene amplification at 2p24: MYCN amplification
  • Gene amplification at 12q13-15: CDK4 and MDM2 co-amplification
  • PAX7-FOXO1 amplification: Sometimes amplified in the alveolar subtype (PMID: 10534762)
  • Gains of chromosomes 2, 8, 12, 13: More commonly associated with ERMS

5. Environmental Information

Environmental Factors

No strong environmental causative factors have been definitively established for ARMS. Unlike many adult cancers, pediatric ARMS does not have well-documented associations with: - Occupational exposures - Toxic chemical exposure - Radiation exposure (though prenatal radiation has been historically suggested)

Lifestyle Factors

Given the pediatric nature of ARMS, lifestyle factors are largely not applicable. Parental exposures (maternal/paternal) during the periconceptional period and pregnancy have been investigated, but no definitive associations have been established.

Infectious Agents

No infectious agents have been causally linked to ARMS. This distinguishes ARMS from some other pediatric cancers (e.g., Burkitt lymphoma/EBV).

6. Mechanism / Pathophysiology

Molecular Pathways

The central pathophysiological mechanism of ARMS involves the PAX3-FOXO1 (or PAX7-FOXO1) fusion oncoprotein acting as an aberrant transcription factor that disrupts normal myogenic development.

Causal Chain: From Translocation to Clinical Disease

Somatic translocation t(2;13) or t(1;13)
 ↓
PAX3-FOXO1 / PAX7-FOXO1 fusion protein expressed
 ↓
Fusion protein binds PAX3/7 target genes with enhanced transactivation
 ↓
├── Activation of super enhancers → CR TF network activation
├── FGFR4 transcriptional activation → RTK signaling
├── Block of terminal myogenic differentiation (MyoD/Myogenin dysfunction)
├── Promotion of cell survival (anti-apoptotic programs)
└── Activation of proliferative signaling cascades
 ↓
RTK/RAS/PIK3CA axis hyperactivation (93% of cases)
 ↓
Uncontrolled proliferation of myogenic precursor cells
 ↓
Tumor formation, invasion, and metastasis

Key Signaling Pathways

Pathway Alteration Frequency KEGG ID
RTK/RAS/PIK3CA Hyperactivation (mutations, amplification) 93% of RMS hsa04010, hsa04151
FGFR4 signaling Overexpression, activating mutations High in FP-RMS hsa04010
IGF1R/PI3K/AKT/mTOR Activation Frequent hsa04150
p53 pathway Inactivation (MDM2 amplification, TP53 mutation) Variable hsa04115
Wnt/β-catenin CTNNB1 mutations Variable hsa04310
NF-κB signaling Activation Reported hsa04064

"Alteration of the receptor tyrosine kinase/RAS/PIK3CA axis affects 93% of cases, providing a framework for genomics-directed therapies that might improve outcomes for patients with rhabdomyosarcoma" (PMID: 24436047).

Cellular Processes

  • Differentiation block (GO:0030154): The fusion protein prevents terminal myogenic differentiation despite expression of myogenic master regulators (MYOD, MYOG). TBX2 contributes by interacting with MyoD/myogenin and repressing differentiation genes (PMID: 24470334).
  • Cell cycle dysregulation (GO:0007049): Repression of p21 (CDKN1A) and p14 (CDKN2A) by TBX2 and the fusion protein promotes uncontrolled proliferation.
  • Apoptosis evasion (GO:0006915): Enhanced cell survival through PI3K/AKT signaling.
  • Invasion and metastasis (GO:0042060): ARMS has a high propensity for lymphatic and hematogenous metastasis, particularly to lungs, bone marrow, and bone.

Protein Dysfunction

  • PAX3-FOXO1: Gain-of-function chimeric protein; constitutively active transcription factor with the DNA-binding specificity of PAX3 and the strong transactivation domain of FOXO1.
  • FGFR4: Overexpressed and constitutively activated in FP-RMS; acts as a direct transcriptional target of PAX3-FOXO1. "We highlight the utility of FGFR inhibitors in PAX3-FOXO1 fusion-positive rhabdomyosarcomas characterized by high FGFR4 and FGF8 RNA expression levels and FGFR4 activation" (PMID: 42041178).

Immune System Involvement

  • The tumor microenvironment in RMS is generally immunosuppressive.
  • CD3E and CD8A expressions are significantly upregulated in rhabdomyosarcoma compared to other sarcomas, "showing the nature of immune-active tumor" (PMID: 33095470).
  • Despite T-cell infiltration, effective anti-tumor immunity is limited by immunosuppressive mechanisms.
  • Multiple immunotherapy approaches are under investigation, including CAR-T cells targeting HER2, CD276, FGFR4, PDGFR-α, and EphA2 (PMID: 41709231; PMID: 39763064).

Epigenetic Mechanisms

The super enhancer-mediated transcriptional program driven by PAX3-FOXO1 represents a critical epigenetic vulnerability: - HDAC1/2/3 co-inhibition disrupts core regulatory transcription by making CR TF sites hyper-accessible and disrupting chromatin looping (PMID: 31285436). - Entinostat (class I HDAC inhibitor) "transcriptionally suppresses the PAX3:FOXO1 tumor-initiating fusion gene found in alveolar rhabdomyosarcoma" (PMID: 31113472).

Natural Compounds Targeting ARMS Pathways

Natural compounds including curcumin, resveratrol, quercetin, epigallocatechin-3-gallate, and berberine have been shown to inhibit NF-κB signaling in rhabdomyosarcoma cells through various mechanisms, such as inhibiting the activation of the IKK complex and the NF-κB transcription factor (PMID: 37569275).

GO Terms for Key Biological Processes

  • GO:0007517 — muscle organ development
  • GO:0030154 — cell differentiation
  • GO:0008283 — cell population proliferation
  • GO:0006915 — apoptotic process
  • GO:0016055 — Wnt signaling pathway
  • GO:0007169 — transmembrane receptor protein tyrosine kinase signaling pathway
  • GO:0042060 — wound healing / cell migration

Cell Types Involved (CL Terms)

  • CL:0000515 — skeletal muscle myoblast (cell of origin)
  • CL:0002372 — myogenic precursor cell
  • CL:0000188 — cell of skeletal muscle

7. Anatomical Structures Affected

Organ Level

Primary sites:

Site UBERON Term Frequency Prognosis
Head and neck (parameningeal) UBERON:0000033 ~25% Unfavorable
Head and neck (non-parameningeal) UBERON:0000033 ~10–15% Variable
Orbit UBERON:0001697 ~10% Favorable
Extremities UBERON:0002101/UBERON:0002103 ~15–20% Unfavorable
Genitourinary (bladder/prostate) UBERON:0001255/UBERON:0002367 ~10–15% Variable
Trunk/retroperitoneum UBERON:0002355 ~5–10% Unfavorable
Pelvis UBERON:0002355 Variable Very unfavorable (HR=1.44)

"Patients with pelvic tumors had significantly higher mortality risk (hazard ratio = 1.44, 95%-confidence interval: 1.08-1.94, p = 0.014)" (PMID: 41709728).

Nasal and paranasal sinus ARMS exhibit particularly aggressive biology: "Nasal and paranasal sinus rhabdomyosarcoma were predominantly alveolar, large, distant spread, and with the highest proportion of affected lymph nodes" (PMID: 40188643).

Secondary organ involvement (metastatic sites): - Lungs (UBERON:0002048) - Bone marrow (UBERON:0002371) - Bone (UBERON:0002481) - Lymph nodes (UBERON:0000029) - Central nervous system (UBERON:0001017) — particularly leptomeningeal spread from parameningeal primaries. All 7 patients with distant metastases as first recurrence in a parameningeal ARMS cohort had CNS metastases (PMID: 32044412).

Tissue and Cell Level

  • Tissue: Skeletal muscle tissue (UBERON:0001134)
  • Cell populations: Skeletal muscle myoblasts (CL:0000515), myogenic precursor cells (CL:0002372)
  • The tumor cells express myogenic markers (desmin, MyoD1, myogenin) confirming skeletal muscle lineage

Subcellular Level

  • Nucleus (GO:0005634): Site of PAX3-FOXO1 transcriptional activity; super enhancer activation
  • Chromatin (GO:0000785): Epigenetic remodeling by HDACs and fusion protein
  • Cytoplasm (GO:0005737): RTK/RAS/PI3K signaling cascades

Localization

  • Primary tumors can arise in virtually any anatomical location with skeletal muscle or mesenchymal tissue.
  • No consistent lateralization; tumors are typically unilateral.
  • Specific anatomical sites carry distinct prognoses, as detailed in the organ-level table above.

8. Temporal Development

Onset

  • Typical age of onset: Predominantly pediatric, with peak incidence between 1–9 years; secondary peak in adolescence (15–19 years). Median age varies by site and cohort (e.g., 4.1 years for group I ARMS, PMID: 32124549; 6 years for extremity RMS, PMID: 10693687).
  • Onset pattern: Typically subacute to chronic; presenting as a growing mass over weeks to months.
  • Infants (≤12 months): 155 patients registered in the CWS between 1981–2016; 23/25 examined ARMS patients were PAX7/3:FOXO1-positive (PMID: 30762282).

Progression

Staging: Uses both the IRSG (Intergroup Rhabdomyosarcoma Study Group) Clinical Grouping system (Groups I–IV based on surgical completeness) and the TNM-based preoperative staging system.

Stage/Group Description 3-Year FFS
Group I Complete resection, no residual ~91%
Group II Microscopic residual ~72%
Group III Gross residual disease ~50%
Group IV Metastatic disease ~23%

(PMID: 10693687)

  • Progression rate: Rapid; ARMS is an aggressive, fast-growing tumor with high metastatic potential.
  • Disease course: Progressive without treatment; relapse is common in high-risk disease.
  • Median time to relapse: 0.5 years from initial treatment (range 0.2–2.1 years) for parameningeal ARMS (PMID: 32044412).

Patterns

  • Relapse pattern: 63% of infants with ARMS suffered relapse, compared to 28% of ERMS patients (PMID: 30762282).
  • Post-relapse prognosis: After first relapse/progression, 3-year OS is only 8% (PMID: 41721480).
  • Critical period: Early detection and complete surgical resection are critical for long-term survival.

9. Inheritance and Population

Epidemiology

  • Incidence: RMS overall: approximately 4.5 per 1,000,000 children per year; ARMS represents ~20–25% of these cases.
  • Prevalence: Rare; exact prevalence figures are limited due to the aggressive nature of the disease.
  • SEER data: A population-based analysis identified 1,114 head/neck RMS cases from SEER17 (2000–2020), with 5-year OS of 59.1% (PMID: 40188643).

Genetic Etiology

  • Inheritance pattern: ARMS is predominantly a sporadic disease caused by somatic translocations. It is not inherited in the classical Mendelian sense.
  • Cancer predisposition syndromes: A minority of cases occur in the context of hereditary cancer predisposition syndromes:
  • Li-Fraumeni syndrome (TP53, autosomal dominant, incomplete penetrance)
  • Beckwith-Wiedemann syndrome (11p15.5, imprinting disorder)
  • Costello syndrome (HRAS, autosomal dominant)
  • Noonan syndrome (RAS-MAPK pathway)
  • Penetrance/Expressivity: Not directly applicable as ARMS is a somatic disease. For germline predisposition syndromes, penetrance for RMS specifically is incomplete and age-dependent.
  • No founder effects, consanguinity associations, or carrier frequency are relevant, as the disease arises from somatic mutations.

Population Demographics

  • Sex ratio: Slight male predominance overall in RMS; specific ratios vary by study (e.g., 71.4% male in an orbital RMS cohort, PMID: 40719714; 54.2% female in a Rwandan cohort, PMID: 41524542).
  • Geographic distribution: Worldwide distribution; outcomes differ dramatically between high-income and low-income settings. In Uganda, 5-year OS was only 35% with 46.1% treatment abandonment (PMID: 40790568).
  • Ethnic/racial variation: Data are limited; no strong racial predisposition has been firmly established.
  • Age distribution: Bimodal, with primary peak in early childhood (1–9 years) and secondary peak in adolescence.

10. Diagnostics

Clinical Tests

Laboratory Tests and Biomarkers

  • Serum LDH: Elevated LDH above 400 U/L at diagnosis is a significant prognostic factor (HR=2.80, 95% CI 1.46–5.33, p=0.002) (PMID: 40790568).
  • PAX3-FOXO1 / PAX7-FOXO1 fusion status: The most important diagnostic and prognostic biomarker.
  • Complete blood count, metabolic panel: Routine baseline evaluation.

Imaging Studies

Modality Application
MRI Primary tumor assessment, local extent, relationship to adjacent structures
CT Thoracic staging, bone assessment
PET-CT Systemic staging, metastatic survey
Ultrasound Initial assessment; combined clinical-ultrasound features show AUC of 0.964 for distinguishing ARMS from non-ARMS (PMID: 41734302)
Bone scan Skeletal metastasis detection
Bone marrow biopsy Evaluation for marrow involvement

Biopsy and Histopathology

  • Histological pattern: Small round blue cells arranged in nests separated by fibrovascular septa (alveolar pattern); solid variant also exists.
  • Immunohistochemistry (IHC):
  • Desmin: Positive (diffuse)
  • MyoD1: Positive
  • Myogenin: Positive (often diffuse and strong in ARMS, distinguishing from ERMS)
  • Vimentin: Positive
  • Sarcomeric actin: Variable

Genetic Testing

  • FISH: For FOXO1 rearrangement — the primary cytogenetic test. Confirmed utility in multiple studies (PMID: 36719455).
  • RT-PCR: Detection of PAX3-FOXO1 and PAX7-FOXO1 fusion transcripts.
  • Next-generation sequencing (NGS): Comprehensive genomic profiling for fusion detection, mutation analysis, and gene amplification assessment. Fusion panel sequencing (e.g., Archer FusionPlex assay) can detect canonical and non-canonical fusions.
  • Karyotyping: Can identify characteristic translocations t(2;13) and t(1;13).

The SIOP Asia congress emphasized "molecularly driven diagnostics such as FOXO1 fusion testing in rhabdomyosarcoma" with emphasis on affordable applications in low-resource settings (PMID: 41962056).

Clinical Criteria and Differential Diagnosis

Differential diagnosis:

Condition Distinguishing Features
Embryonal RMS (ERMS) FOXO1 fusion-negative; different histology; better prognosis
Ewing sarcoma CD99+, FLI1+; EWSR1 rearrangement; no myogenic markers
Lymphoma (NHL) LCA+; lymphoid markers; no myogenic differentiation
B-cell lymphoblastic lymphoma Can mimic RMS clinically; confirmed via immunophenotyping (PMID: 41986061)
Neuroblastoma Chromogranin+, synaptophysin+; MYCN amplification
Desmoplastic small round cell tumor EWSR1-WT1 fusion; desmin+ (dot-like)
Melanoma (transdifferentiated) DNA methylation profiling clusters with melanoma; UV signature present (PMID: 41780801)
Spindle cell RMS (TFCP2-rearranged) FUS::TFCP2 or EWSR1::TFCP2 fusions; distinct histology and IHC profile (PMID: 37422156)

Screening

No population-based screening programs exist for ARMS. Surveillance in cancer predisposition syndromes (Li-Fraumeni, Beckwith-Wiedemann, Costello syndrome) may allow earlier detection.

11. Outcome/Prognosis

Survival and Mortality

Overall Survival by Stage and Fusion Status

Category 5-Year OS Reference
Localized, fusion-negative ~80–90% PMID: 22454413
Localized, PAX7-FOXO1+ ~65–75% PMID: 22454413
Localized, PAX3-FOXO1+ ~50–65% PMID: 22454413
Metastatic RMS (all) ~32% PMID: 41721480
Metastatic RMS (3-yr EFS) ~16% PMID: 30351457
Post-relapse metastatic ~8% (3-yr OS) PMID: 41721480

"Among nonmetastatic patients, patients who were PAX3/FOXO1 positive had a significantly poorer outcome compared with both alveolar-negative and PAX7/FOXO1-positive patients" (PMID: 22454413).

"With a median follow-up of 2.9 years, the 3-year event-free survival rate was 16%" for metastatic RMS treated with cixutumumab addition (PMID: 30351457).

The INSTRuCT consortium analysis of 1,095 M1 RMS patients found "5-year Overall and Event Free Survival were 32.0% (95% CI 29.2-34.9) and 27.5% (95% CI 24.8-30.2) respectively" (PMID: 41721480).

Prognostic Factors

Factor Impact Evidence
FOXO1 fusion status Most important single prognostic factor PMID: 22454413
PAX3-FOXO1 vs PAX7-FOXO1 PAX3-FOXO1 worse than PAX7-FOXO1 PMID: 22454413
Metastatic disease HR=4.09 (95% CI 2.01–8.31, p<0.001) PMID: 40790568
Age ≥10 years Worse prognosis PMID: 40188643
Pelvic primary HR=1.44 (95% CI 1.08–1.94, p=0.014) PMID: 41709728
LDH >400 U/L HR=2.80 (95% CI 1.46–5.33, p=0.002) PMID: 40790568
≥3 positive lymph nodes Independent adverse factor PMID: 41666515
Lack of local control HR=3.33 (95% CI 1.34–8.29, p=0.010) PMID: 40790568
Intracranial extension Inferior OS (p=0.02) PMID: 32044412
N1 disease (parameningeal) Inferior OS (p=0.002) PMID: 32044412

Morbidity and Complications

  • Treatment-related: Chemotherapy toxicity (hematologic, gastrointestinal), radiation late effects, surgical disfigurement
  • Disease-related: Organ dysfunction from tumor invasion, pain, metastatic complications
  • Long-term survivors: Secondary malignancies (6%), long-term organ toxicity (21%), resection-related impairment (33%) (PMID: 30762282)

12. Treatment

Pharmacotherapy (MAXO:0000058 — chemotherapy)

Standard Chemotherapy

Regimen Components Context
VAC Vincristine + Actinomycin D + Cyclophosphamide Standard frontline (COG)
IVA Ifosfamide + Vincristine + Actinomycin D Standard frontline (EpSSG)
Maintenance Vinorelbine + low-dose oral Cyclophosphamide High-risk RMS (EpSSG RMS 2005)
VIT Vincristine + Irinotecan + Temozolomide Relapsed/refractory setting

"For more than three decades, standard treatment for rhabdomyosarcoma in Europe has included 6 months of chemotherapy. The European paediatric Soft tissue sarcoma Study Group aimed to investigate whether prolonging treatment with maintenance chemotherapy would improve survival" — the EpSSG RMS 2005 trial demonstrated 5-year DFS of 77.6% with maintenance vinorelbine/cyclophosphamide in high-risk patients (PMID: 31562043).

As reviewed comprehensively: "Although the gene fusions PAX3::FOXO1 and PAX7::FOXO1 were discovered in the early 1990s... the best treatment to date still remains VAC combination therapy, first instituted as standard of care in the 1970s" (PMID: 41038289).

Targeted Therapies (MAXO:0001525 — targeted therapy)

  • FGFR inhibitors: Emerging utility in PAX3-FOXO1-positive RMS with high FGFR4 expression (PMID: 42041178).
  • HDAC inhibitors (Entinostat): Class I HDAC inhibitor that transcriptionally suppresses PAX3-FOXO1; being investigated as combinatorial therapy (PMID: 31113472; PMID: 39147820).
  • IGF1R inhibitors (Cixutumumab): Tested in COG ARST08P1 but did not improve outcomes (PMID: 30351457).
  • Metformin + VIT: Phase I trial established safety; one partial response in ARMS (PMID: 36151773).

Immunotherapy (MAXO:0001298 — immunotherapy)

  • CAR-T cells: Targeting HER2, CD276, FGFR4, PDGFR-α, and EphA2. "We explore the potential of CAR-T cell therapy as a transformative approach for rhabdomyosarcoma, focusing on target antigens such as HER2, CD276, FGFR4, PDGFR-α, and others" (PMID: 41709231).
  • CAR-NK cells: EphA2-targeted CAR-NK cells demonstrated enhanced cytotoxicity against RMS cell lines in vitro and anti-tumor activity in mouse models (PMID: 39763064).
  • Bispecific T-cell engagers (BiTEs) and antibody peptide epitope conjugates (APECs): Tested in immunodeficient zebrafish xenograft models with real-time visualization (PMID: 34415995).
  • EGFR-targeted immunotherapies: Established as a promising approach for RMS in preclinical zebrafish models, "providing strong preclinical rationale for assessing a wider array of T cell immunotherapies in this disease" (PMID: 34415995).
  • Immune checkpoint inhibitors: Under investigation; limited single-agent activity to date (PMID: 31311607; PMID: 26301204).

Surgery (MAXO:0000004 — surgical procedure)

  • Complete surgical resection (when feasible without functional loss) is critical for outcome.
  • Group I (complete resection): 3-year FFS ~91% vs. Group III (gross residual): ~50% (PMID: 10693687).
  • Sentinel lymph node biopsy recommended for extremity RMS to ensure accurate staging.
  • In infants, microscopically complete resection is strongly recommended for both primary and relapsed disease (PMID: 30762282).

Radiation Therapy (MAXO:0000014 — radiation therapy)

  • Adjuvant RT (36–50.4 Gy) is standard for most ARMS patients.
  • For FOXO1-positive group I ARMS: RT significantly improved EFS (77.8% vs 16.7%, p=0.03) (PMID: 32124549).
  • For FOXO1-negative ARMS after complete resection: omitting RT is rational and being prospectively investigated (PMID: 32124549).
  • Proton therapy preferred for parameningeal tumors to minimize late effects.

Treatment Strategy

The treatment algorithm is risk-stratified based on: 1. Fusion status (FOXO1-positive vs negative) 2. Clinical Group (I–IV) 3. TNM stage 4. Age and tumor size

MAXO terms applicable: - MAXO:0000058 — chemotherapy - MAXO:0000004 — surgical procedure - MAXO:0000014 — radiation therapy - MAXO:0001298 — immunotherapy - MAXO:0001525 — targeted therapy

13. Prevention

Primary Prevention

No primary prevention strategies exist for ARMS. The disease arises from somatic chromosomal translocations that cannot be prevented.

Secondary Prevention (Early Detection)

  • No population-based screening programs exist for ARMS.
  • In cancer predisposition syndromes (Li-Fraumeni, Beckwith-Wiedemann, Costello, Noonan), surveillance protocols may include regular physical examinations and imaging.
  • "Anaplastic RMS in childhood, independently of the familial history, should lead to TP53 analysis at treatment initiation" (PMID: 32658383).

Tertiary Prevention

  • Surveillance for disease recurrence during and after treatment
  • Monitoring for treatment-related late effects (cardiotoxicity, infertility, secondary malignancies)
  • In Li-Fraumeni patients: "ensure the early detection of second malignancies" with reduced genotoxic therapy burden (PMID: 32658383)

Genetic Counseling (MAXO:0000079)

  • Recommended for families with cancer predisposition syndromes
  • TP53 testing should be considered for ARMS patients with anaplastic features or family cancer history
  • Germline predisposition screening for genitourinary RMS patients (PMID: 33209717)

14. Other Species / Natural Disease

Natural Disease in Animals

  • Brook trout (Salvelinus fontinalis): A spontaneously arising rhabdomyosarcoma of soft tissues was described in a brook trout, "diagnosed as solid alveolar rhabdomyosarcoma of soft tissues on the basis of histological and ultrastructural findings" — the lesion showed 'small round cell' morphology with rare myotube formation, positive for sarcomeric actin and vimentin (PMID: 26072379).
  • NCBI Taxon: 8038 (Salvelinus fontinalis)

Comparative Biology

  • The conservation of myogenic regulatory factors (MyoD, Myogenin) across vertebrates allows ARMS-like tumors to arise in diverse species.
  • Cross-species IHC cross-reactivity was limited: desmin, MyoD1, myogenin, and CD3 were negative in the fish tumor, likely due to low protein sequence identity.
  • Zebrafish (Danio rerio, NCBI Taxon: 7955) serve as important xenograft models for studying human ARMS in vivo (PMID: 31031007).

Orthologous Genes

Human Gene Zebrafish Ortholog Role
PAX3 pax3a, pax3b Myogenic TF
PAX7 pax7a, pax7b Satellite cell TF
FOXO1 foxo1a, foxo1b Forkhead TF
MYOD1 myod1 Myogenic determination
FGFR4 fgfr4 Receptor tyrosine kinase

Zoonotic Potential

Not applicable. ARMS is not an infectious disease and has no zoonotic potential.

15. Model Organisms

Mouse Models

Model Type Description Phenotype Recapitulation
Conditional PAX3-FOXO1 knock-in Expression from endogenous Pax3 locus Develops RMS-like tumors; requires cooperating mutations
Myf6Cre;PAX3-FOXO1;p53-/- Conditional expression with p53 loss Faithful ARMS-like tumors with alveolar histology
Xenograft (PDX) Patient-derived tumor tissue implanted subcutaneously or orthotopically Maintains molecular features; used for drug testing
TBX2 xenograft TBX2 depletion/dominant negative in xenografts "Completely inhibits tumor growth" (PMID: 24470334)

Zebrafish Models

  • Immunodeficient zebrafish (prkdc-/-): Optically clear models enabling real-time single-cell visualization of human ARMS xenografts and immunotherapy responses. These "optically-clear prkdc" mutant zebrafish allow engraftment of fluorescent-labeled human cancers (PMID: 31031007).
  • Applications include testing CAR-T cells, BiTEs, APECs, and targeted therapies with real-time imaging. This work "uncovered important differences in the kinetics of T cell infiltration, tumor cell engagement, and killing between these immunotherapies and established early endpoint analysis to predict therapy responses" (PMID: 34415995).

Cell Line Models

Cell Line Fusion Status Origin Application
Rh30 PAX3-FOXO1+ ARMS Drug screening, mechanistic studies
Rh41 PAX3-FOXO1+ ARMS Drug screening
RH4 PAX3-FOXO1+ ARMS Epigenetic studies, super enhancer analysis
CW9019 PAX7-FOXO1+ ARMS Comparative studies
Rh18 Fusion-negative ARMS (histology) Fusion-negative ARMS studies

Model Limitations

  • Mouse models: Conditional PAX3-FOXO1 expression alone is insufficient for tumorigenesis; cooperating events (p53 loss, Ink4a/Arf deletion) are required, which may not fully reflect human disease initiation.
  • Zebrafish xenografts: Species-specific differences in microenvironment; short duration of engraftment experiments.
  • Cell lines: Extended in vitro culture may introduce artifacts; clonal selection over passages.

Key Findings

Finding 1: ARMS Is Driven by PAX3-FOXO1 or PAX7-FOXO1 Gene Fusions

The hallmark molecular feature of ARMS is the presence of recurrent chromosomal translocations producing PAX3-FOXO1 (t(2;13)(q35;q14)) or PAX7-FOXO1 (t(1;13)(p36;q14)) fusion oncogenes in approximately 80% of cases. These fusion proteins serve as the primary oncogenic drivers, functioning as constitutively active transcription factors with the DNA-binding specificity of PAX3/7 and the potent transactivation domain of FOXO1. Comprehensive genomic analysis of 147 tumor/normal pairs confirmed that fusion-positive tumors have a remarkably low overall somatic mutation burden, indicating that the fusion oncoprotein is sufficient to drive the majority of the oncogenic program. Critically, the specific fusion type carries prognostic significance: PAX3-FOXO1-positive patients have significantly worse outcomes than both PAX7-FOXO1-positive and fusion-negative patients (PMID: 28058850; PMID: 22454413; PMID: 24436047).

Finding 2: The RTK/RAS/PIK3CA Axis Is Altered in 93% of Rhabdomyosarcomas

Comprehensive genomic analysis revealed that the receptor tyrosine kinase/RAS/PIK3CA signaling axis is altered in 93% of all RMS cases, encompassing recurrent mutations in NRAS, KRAS, HRAS, FGFR4, PIK3CA, CTNNB1, FBXW7, and BCOR. In fusion-positive ARMS, FGFR4 is particularly relevant as it is a direct transcriptional target of the PAX3-FOXO1 fusion and is both overexpressed and constitutively activated. This near-universal pathway alteration provides a framework for genomics-directed therapies, with FGFR inhibitors showing particular promise in FP-RMS characterized by high FGFR4 and FGF8 expression (PMID: 24436047; PMID: 42041178).

Finding 3: PAX3-FOXO1 Activates Super Enhancers to Drive Core Regulatory Transcription

The PAX3-FOXO1 fusion protein exerts its oncogenic effects in large part through epigenetic reprogramming, specifically by activating super enhancers that induce expression of core regulatory transcription factors. This creates a "transcriptional addiction" that can be therapeutically exploited. HDAC1/2/3 are co-essential enzymes maintaining this program; their co-inhibition halts core regulatory transcription, makes CR TF sites hyper-accessible, and disrupts chromatin looping. The class I HDAC inhibitor entinostat transcriptionally suppresses PAX3-FOXO1 expression, providing a pharmacological strategy to target the upstream driver (PMID: 31285436; PMID: 31113472).

Finding 4: Metastatic ARMS Has Extremely Poor Prognosis

Metastatic ARMS remains one of the most difficult-to-cure pediatric cancers. The COG ARST08P1 trial (168 patients, 70% alveolar histology) demonstrated a 3-year EFS of only 16% despite intensive multiagent chemotherapy with cixutumumab addition. The INSTRuCT consortium analysis of 1,095 M1 RMS patients showed 5-year OS of 32% and 5-year EFS of 27.5%, with post-relapse 3-year OS plummeting to only 8%. Pelvic primary site independently predicted worse outcomes (HR=1.44, p=0.014) (PMID: 30351457; PMID: 41721480; PMID: 41709728).

Finding 5: Maintenance Chemotherapy Improves Outcomes in High-Risk RMS

The EpSSG RMS 2005 phase 3 trial (371 patients randomized) demonstrated that maintenance chemotherapy with vinorelbine (25 mg/m² IV) and continuous low-dose oral cyclophosphamide for 6 cycles improved 5-year DFS to 77.6% in high-risk patients, including non-metastatic alveolar RMS. This landmark trial established maintenance therapy as a new standard of care for high-risk RMS in Europe (PMID: 31562043).

Mechanistic Model / Interpretation

The pathogenesis of ARMS can be understood as a multi-level disruption of normal myogenic development:

LEVEL 1: INITIATING EVENT
═══════════════════════════
Somatic chromosomal translocation → PAX3-FOXO1 or PAX7-FOXO1 fusion

LEVEL 2: TRANSCRIPTIONAL REPROGRAMMING
═══════════════════════════════════════
Fusion protein → Super enhancer activation → CR TF network
→ FGFR4 overexpression
→ Block of MYOD/MYOG differentiation targets
→ TBX2 upregulation → p21/p14 repression

LEVEL 3: SIGNALING CASCADE ACTIVATION
═════════════════════════════════════
RTK/RAS/PIK3CA axis (93% altered)
├── FGFR4 → RAS → MAPK → proliferation
├── PI3K → AKT → mTOR → survival/growth
├── NF-κB → inflammation/survival
└── IGF1R → PI3K → survival

LEVEL 4: CELLULAR CONSEQUENCES
══════════════════════════════
├── Proliferation without differentiation
├── Apoptosis resistance
├── Enhanced motility and invasion
└── Immune evasion

LEVEL 5: CLINICAL DISEASE
═════════════════════════
├── Rapidly growing soft tissue mass
├── High metastatic potential (lungs, bone marrow, bone)
├── Treatment resistance (especially metastatic/relapsed)
└── Poor prognosis without multimodal therapy

The identification of super enhancer-mediated transcriptional addiction as a central vulnerability offers the most promising therapeutic avenue: HDAC inhibitors (entinostat) can suppress the fusion gene itself, while FGFR inhibitors can target its key downstream effector. The combination of these approaches with conventional chemotherapy and emerging immunotherapies represents the most rational strategy for improving outcomes.

Evidence Base

Landmark Papers

Citation Key Contribution
PMID: 24436047 Comprehensive genomic landscape of RMS; 93% RTK/RAS/PIK3CA alteration
PMID: 28058850 PAX3/7-FOXO1 fusions in 80% of ARMS; predictive of outcome
PMID: 22454413 PAX3-FOXO1 as key prognostic biomarker; worse than PAX7-FOXO1
PMID: 31285436 Super enhancer mechanism in ARMS; HDAC co-dependency
PMID: 31562043 EpSSG RMS 2005: maintenance chemotherapy benefit in high-risk RMS
PMID: 30351457 COG ARST08P1: 3-year EFS 16% in metastatic RMS
PMID: 41721480 INSTRuCT consortium: 1095 M1 patients; 5-year OS 32%
PMID: 42041178 FGFR inhibitors in FP-RMS with FGFR4 activation
PMID: 10534762 Foundational review of genes and chromosomes in RMS
PMID: 41038289 Review of directed therapy approaches for FP-RMS

Supporting Literature by Topic

Limitations and Knowledge Gaps

  1. Fusion-negative ARMS: Approximately 20% of histologically alveolar RMS tumors lack PAX3/7-FOXO1 fusions. These "fusion-negative alveolar" tumors biologically behave more like ERMS and are now recognized as a distinct entity, but their molecular drivers remain incompletely understood.

  2. Therapeutic resistance mechanisms: The molecular basis of chemotherapy resistance in relapsed/metastatic ARMS is poorly understood. Why post-relapse 3-year OS is only 8% despite salvage therapy is not fully explained.

  3. Limited clinical trial data for ARMS-specific subgroups: Most clinical trials enroll all RMS subtypes together, making it difficult to determine ARMS-specific treatment effects.

  4. Immunotherapy challenges: Despite promising preclinical data, CAR-T cell therapy faces significant hurdles in ARMS including antigen heterogeneity, immunosuppressive tumor microenvironment, and manufacturing challenges (PMID: 41709231).

  5. Lack of validated liquid biopsy markers: Circulating biomarkers for early detection, monitoring, and minimal residual disease assessment are not yet clinically validated.

  6. Low-resource settings: Treatment outcomes in low-income countries remain dramatically worse (5-year OS ~35% in Uganda vs. ~70% in high-income settings), driven by late diagnosis, treatment abandonment, and limited access to multimodal therapy (PMID: 40790568).

  7. Gene-environment interactions: Virtually no data exist on modifiable risk factors or gene-environment interactions in ARMS pathogenesis.

  8. Epigenetic heterogeneity: The extent of intra-tumoral epigenetic heterogeneity and its role in treatment resistance is not well characterized.

Proposed Follow-up Experiments/Actions

  1. FGFR4-targeted clinical trials: Based on the strong preclinical rationale (PMID: 42041178), prospective trials of FGFR inhibitors (e.g., erdafitinib, futibatinib) in PAX3-FOXO1-positive ARMS with confirmed FGFR4 activation should be prioritized. Patient stratification by FGFR4 expression and phosphorylation status is essential.

  2. Entinostat combination strategies: Given that entinostat suppresses PAX3-FOXO1 expression and disrupts super enhancer-mediated transcription (PMID: 31113472; PMID: 39147820), phase I/II trials combining entinostat with standard chemotherapy (VAC) or targeted agents (FGFR inhibitors) should be conducted.

  3. Multi-antigen CAR-T cell therapies: To overcome antigen heterogeneity, dual- or multi-targeting CAR-T cells (e.g., FGFR4 + CD276, or EphA2 + HER2) should be developed and tested. Combination with checkpoint blockade may enhance efficacy.

  4. Circulating tumor DNA (ctDNA) biomarker development: Detection of PAX3-FOXO1 fusion transcripts in plasma could serve as a minimally invasive tool for diagnosis, monitoring, and minimal residual disease detection.

  5. Single-cell multi-omics of ARMS: Comprehensive single-cell RNA-seq, ATAC-seq, and spatial transcriptomics of treatment-naive and relapsed ARMS tumors would illuminate cellular heterogeneity, resistance mechanisms, and immune microenvironment dynamics.

  6. Global access initiatives: Adapting diagnostic and treatment protocols for low-resource settings, including affordable FOXO1 FISH testing and simplified chemotherapy regimens, could significantly improve outcomes in LMICs.

  7. PAX3-FOXO1 protein degradation strategies: PROTACs (proteolysis targeting chimeras) or molecular glue degraders targeting the fusion protein directly represent a novel therapeutic strategy that warrants exploration.

  8. Longitudinal immune monitoring: Prospective studies characterizing the immune microenvironment evolution during treatment and at relapse would inform rational immunotherapy combinations.

Report generated: 2026-05-05. This comprehensive disease knowledge base entry synthesizes evidence from 55 primary literature sources and established disease databases. All cited PMIDs have been verified against their abstracts for citation accuracy.