Thymoma

Neoplastic MONDO:0006456 Pathograph 14 Show in embeddings browser thymic epithelial neoplasm

Thymoma is a thymic epithelial tumor of the anterior mediastinum that is best modeled in dismech as one disease-level mechanism graph with histologic and invasion-status subtype facets rather than separate disease pages. Thymomas have a lower mutational burden than thymic carcinoma, are enriched for GTF2I mutations in WHO type A and AB tumors, and uniquely perturb thymic selection programs so that impaired central tolerance drives autoimmune syndromes such as myasthenia gravis, pure red cell aplasia, and Good syndrome. That same tolerance defect makes thymoma an outlier for checkpoint-inhibitor toxicity: severe immune-related adverse events are more than three times as frequent in thymoma as in thymic carcinoma treated with the same agents, so the toxicity is modeled here as a therapy-unmasked branch of the tolerance-failure chain rather than as an unrelated drug side effect.

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Mappings
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Pathophys.
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Histopath.
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Phenotypes
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Gaps
14
Pathograph
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Genes
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Medical Actions
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Subtypes
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Differentials
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Datasets
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Deep Research
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Classifications

Harrison's Part
ONCOLOGY HEMATOLOGY IMMUNE RHEUMATOLOGIC
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Mappings

MONDO
MONDO:0006456 thymoma
skos:exactMatch MONDO
NCIT
NCIT:C3411 Thymoma
skos:exactMatch NCIT
NCIT
NCIT:C3411 Thymoma
skos:exactMatch NCIT
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Subtypes

7
histological pattern
Type A thymoma NCIT:C6454
Spindle-cell thymoma with relatively indolent clinical behavior and marked enrichment for GTF2I mutation.
Show evidence (1 reference)
PMID:24974848 SUPPORT Human Clinical
"We analyzed 28 thymic epithelial tumors (TETs) using next-generation sequencing and identified a missense mutation (chromosome 7 c.74146970T>A) in GTF2I at high frequency in type A thymomas, a relatively indolent subtype."
Human tumor sequencing links WHO type A thymoma to indolent biology and a strong GTF2I-mutant state.
Type AB thymoma NCIT:C6885
Mixed spindle-cell and lymphocyte-rich thymoma that shares much of the GTF2I-enriched molecular profile of type A thymoma.
Show evidence (1 reference)
PMID:24974848 SUPPORT Human Clinical
"In a series of 274 TETs, we detected the GTF2I mutation in 82% of type A and 74% of type AB thymomas but rarely in the aggressive subtypes, where recurrent mutations of known cancer genes have been identified."
Large human tumor series supports type AB thymoma as part of the GTF2I-enriched, less aggressive facet of thymoma.
Type B1 thymoma NCIT:C6887
Cortical-like thymoma rich in immature T lymphocytes, generally showing less invasion than type B3 thymoma.
Show evidence (1 reference)
PMID:15063231 SUPPORT Human Clinical
"The frequency of invasion to neighboring organs increased according to tumor subtype in the order A (0%), AB (6%), B1 (19%), B2 (25%), B3 (42%), and C (89%)."
Positions type B1 on the invasion gradient below B2 and B3, supporting its intermediate place on the histologic subtype axis.
Type B2 thymoma NCIT:C6888
Cortical thymoma with numerous lymphocytes and more conspicuous neoplastic epithelial cells; often associated with myasthenia gravis. It is the single most frequently assigned WHO histotype among thymomas.
Show evidence (1 reference)
PMID:25521402 SUPPORT Human Clinical
"WHO type B2 was the most frequent histologic classification among thymomas, whereas squamous was the most common among thymic carcinomas."
The ITMIG international database establishes type B2 as the most common thymoma histotype, supporting its prominence on the histologic subtype axis.
Type B3 thymoma NCIT:C7997
Epithelial-predominant thymoma with higher local invasiveness and worse disease-free survival than type A/AB and B1/B2 thymomas.
Show evidence (2 references)
PMID:15063231 SUPPORT Human Clinical
"The frequency of invasion to neighboring organs increased according to tumor subtype in the order A (0%), AB (6%), B1 (19%), B2 (25%), B3 (42%), and C (89%)."
Human surgical series supports higher invasive propensity in type B3 thymoma than in lower-grade WHO thymoma histotypes.
PMID:15063231 SUPPORT Human Clinical
"The disease-free survival rates were 100% for types A and AB, 83% for types B1 and B2, 36% for type B3, and 28% for type C thymoma at 10 years."
Long-term follow-up supports the prognostic distinction of type B3 within the thymoma histologic axis.
invasion status
Encapsulated thymoma NCIT:C7386
Organ-confined thymoma without gross invasion, generally corresponding to a more resectable and clinically indolent presentation.
Show evidence (1 reference)
PMID:15063231 SUPPORT Human Clinical
"The frequency of invasion to neighboring organs increased according to tumor subtype in the order A (0%), AB (6%), B1 (19%), B2 (25%), B3 (42%), and C (89%)."
Supports a substantial non-invasive, organ-confined population within thymoma (no invasion at all in type A), which is what the encapsulated pole of this axis captures. Marked PARTIAL because the series reports invasion frequency by histotype rather than encapsulation status directly.
Invasive thymoma NCIT:C7904
Thymoma that invades neighboring structures or disseminates intrathoracically and more often requires multimodal treatment.
Show evidence (1 reference)
PMID:20207296 SUPPORT Other
"Their clinical behaviour varies widely, from a relative indolence to the potential of lymph node and/or systematic metastases."
Review-level evidence supports an invasion-status facet within thymoma that is distinct from WHO histologic subtype.
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Discussions and Knowledge Gaps

3
Why does the Gtf2i-mutant mouse reproduce the thymic epithelial architecture defect of human thymoma without reproducing the autoimmunity that defines the human disease?
HUMAN MODEL MISMATCH OPEN gtf2i_mouse_no_autoimmunity
Attached to
pathophysiology#Impaired thymic epithelial progenitor differentiation
The mouse model recapitulates the upstream half of the dismech causal chain - aberrant thymic architecture, impaired medullary differentiation, a cortex-like epithelial signature - yet TCR repertoire analysis shows intrathymic selection remains efficient and no autoimmunity develops. That matters mechanistically, because the disease-level claim in this entry is that the medulla-poor architecture is what causes tolerance failure. The mouse dissociates the two, implying that either an additional human-specific factor is required (the CTLA-4 and PTPN22 risk polymorphisms reported in thymoma-associated myasthenia gravis are candidates) or that the relevant lesion is the frank neoplastic mass rather than the differentiation skew the transgenic reproduces. Curators should not treat this mouse as evidence for the autoimmunity arm of the graph.
Proposed experiments
Gtf2i L424H on autoimmune-permissive genetic backgrounds
exp_gtf2i_autoimmune_permissive_background
Cross the Gtf2i L424H allele onto autoimmune-permissive backgrounds, or combine it with the CTLA-4 and PTPN22 risk variants reported in human thymoma-associated myasthenia gravis, and re-assess autoantibody development and neuromuscular phenotype. A positive result would show the architecture defect is necessary but not sufficient for autoimmunity.
Direct comparison of transgenic and human thymoma epithelium
exp_gtf2i_mouse_human_epithelium_comparison
Compare TCR repertoire and tissue-restricted antigen expression in the transgenic epithelium against human thymoma tissue, to establish whether the mouse reaches the same degree of AIRE loss and MHC class II reduction that human thymomas show. If it does not, the mismatch is one of degree rather than of species-specific biology.
Show evidence (2 references)
PMID:36175547 SUPPORT Model Organism
"TCR repertoire analysis of the cytopenic T cell compartment indicates efficient intrathymic selection; hence, despite marked homeostatic proliferation of T cell clones, autoimmunity is not observed."
The model's authors state directly that autoimmunity does not develop, establishing the mismatch against the human phenotype.
PMID:36175547 SUPPORT Model Organism
"Thus, our transgenic mouse model recapitulates some aspects of the pathophysiology of a genetically defined type of human thymoma."
The deliberately hedged claim of only partial recapitulation is the authors' own scoping of the model's translational validity.
If reduced MHC class II expression contributes to tolerance failure, why is better-preserved MHC class II expression the feature that actually tracks with the presence of myasthenia gravis?
KNOWLEDGE GAP OPEN mhc_class_ii_mg_paradox
Attached to
pathophysiology#Reduced MHC class II antigen presentation
This entry curates reduced MHC class II antigen presentation as a tolerance-failure mechanism, and that reduction is real and most pronounced in WHO types A and AB. But in the same study, among all the abnormalities assessed, only better-preserved MHC class II levels were significantly associated with the presence of myasthenia gravis - and myasthenia gravis is clinically most frequent in types B1 and B2, not A and AB. A coherent reading is that two requirements pull in opposite directions: escape of autoreactive clones needs defective negative selection, but their activation still needs enough class II to present the neuromuscular autoantigen. This entry currently models only the first. Until this is resolved, the reduced-MHC class-II node should not be read as a monotonic driver of myasthenia gravis risk. Prospective sequencing data point the same way from a different direction: GTF2I mutation, which marks the same A/AB histotypes that carry the lowest class II, is prevalent specifically in patients WITHOUT myasthenia gravis. Any resolution has to account for both observations together.
Proposed experiments
MHC class II expression versus MG status stratified by WHO histotype
exp_mhcii_mg_stratified_by_histotype
Stratify MHC class II expression against myasthenia gravis status within each WHO histotype, so the histotype confound (A and AB have both the lowest class II and the least myasthenia gravis) is separated from any independent effect of class II level on risk.
nmTEC-restricted versus bulk tumour MHC class II
exp_nmtec_restricted_class_ii
Test whether MHC class II expression restricted to the neuromuscular antigen-expressing medullary thymic epithelial cell compartment, rather than bulk tumour class II, is what determines myasthenia gravis risk. This would reconcile the two directions by locating the requirement for class II in a specific niche.
Show evidence (1 reference)
PMID:18567864 SUPPORT Human Clinical
"Among all theses abnormalities, only better preserved expression levels of MHCII (P < 0.001) in thymomas were significantly associated with the presence of MG."
States the observation that runs against a simple reduced-class-II-drives-MG reading, which is what makes this an open question rather than a settled mechanism.
What drives the substantial fraction of thymomas that carry no GTF2I mutation and no other detectable somatic driver?
KNOWLEDGE GAP OPEN gtf2i_wildtype_driver_unknown
Attached to
pathophysiology#GTF2I-driven thymic epithelial transformation
The oncogenic arm of this entry is built almost entirely on GTF2I, which is honest to the evidence but covers only part of the disease. Prospective sequencing with a thymic-tumour-dedicated 77-gene panel found GTF2I mutations in 41 percent of patients and NO mutation at all in 39 percent, and the authors report a pattern of mutually exclusive and co-occurring mutations suggesting that GTF2I-wildtype thymoma has a distinct pathogenesis rather than being a diluted version of the same one. Curators should therefore not extend GTF2I-derived mechanism to thymoma as a whole. The gap is partly technical - epithelial cells were absent from some dissociated tumours, so the driver may be present but unsampled in a lymphocyte-dominated specimen - and partly biological, since a non-mutational (epigenetic or structural) driver would be invisible to a targeted panel by construction.
Proposed experiments
Epithelium-enriched whole-genome and methylome profiling of GTF2I-wildtype thymoma
exp_gtf2i_wildtype_epithelium_enriched_wgs
Apply whole-genome sequencing plus methylation and structural-variant calling to flow-sorted or laser-captured epithelial cells from GTF2I-wildtype thymomas, so that dilution by the abundant non-neoplastic thymocyte compartment cannot mask a driver, and so that non-coding and epigenetic drivers invisible to a targeted panel are within reach.
Show evidence (2 references)
PMID:41405018 SUPPORT Human Clinical
"In 39% of patients, no mutations were found in the 77 genes evaluated."
Quantifies the fraction of thymic epithelial tumours with no identified driver even under dedicated targeted sequencing.
PMID:41405018 SUPPORT Human Clinical
"The absence of epithelial cells in some dissociated tumors highlights the challenge of identifying mutations in a subset of thymic epithelial tumors that lack the GTF2I mutation."
Identifies the sampling artefact that makes part of this gap technical rather than biological, which is what the proposed experiment targets.
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Pathophysiology

9
GTF2I-driven thymic epithelial transformation
Recurrent GTF2I mutation defines a major molecular facet of type A and AB thymoma and promotes thymic epithelial proliferation and transformation.
epithelial cell of thymus CL:0002293 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves epithelial cell of thymus (CL:0002293). CL:0002293 is a cell type from the Cell Ontology.
GTF2I hgnc:4659 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves abnormal GTF2I (hgnc:4659). hgnc:4659 is a gene from the HUGO Gene Nomenclature Committee. ⚠ ABNORMAL
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
thymus UBERON:0002370 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in thymus (UBERON:0002370). UBERON:0002370 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Metabolic stress survival program Mutant TFII-I supports stress-adapted growth states.
Impaired thymic epithelial progenitor differentiation Mutant GTF2I skews bipotent thymic epithelial progenitors away from medullary differentiation.
Show evidence (4 references)
PMID:24974848 SUPPORT Human Clinical
"In a series of 274 TETs, we detected the GTF2I mutation in 82% of type A and 74% of type AB thymomas but rarely in the aggressive subtypes, where recurrent mutations of known cancer genes have been identified."
Human tumor sequencing supports GTF2I mutation as the defining molecular driver of the indolent A/AB thymoma facet.
PMID:32034314 SUPPORT In Vitro
"Our findings identify GTF2I mutation as a new oncogenic driver that is responsible for transformation of thymic epithelial cells."
Cell-based functional evidence directly shows that mutant GTF2I can drive thymic epithelial transformation.
PMID:36049655 SUPPORT Model Organism
"We observed that the Gtf2i mutation impairs development of the thymic medulla and maturation of medullary thymic epithelial cells in young mice and causes tumor formation in the thymus of aged mice."
Conditional knock-in of the human hotspot allele into Foxn1-positive thymic epithelium is sufficient to produce thymoma in vivo, raising the transformation claim above the in vitro evidence alone.
+ 1 more reference
Metabolic stress survival program
Mutant GTF2I rewires glycolytic and stress-response programs, supporting tumor growth and survival under nutrient and DNA-damage stress.
GTF2I hgnc:4659 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves abnormal GTF2I (hgnc:4659). hgnc:4659 is a gene from the HUGO Gene Nomenclature Committee. ⚠ ABNORMAL
glycolytic process GO:0006096 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased glycolytic process (GO:0006096). GO:0006096 is a biological process from the Gene Ontology. ↑ INCREASED
Show evidence (2 references)
PMID:32034314 SUPPORT In Vitro
"Gtf2i L424H knockin cells exhibited cell transformation, aneuploidy, and increase tumor growth and survival under glucose deprivation or DNA damage."
In vitro knock-in experiments support a stress-survival program downstream of mutant GTF2I.
PMID:32034314 SUPPORT In Vitro
"Gtf2i mutation also increased the expression of several glycolytic enzymes, cyclooxygenase-2, and caused modifications of lipid metabolism."
The same in vitro study supports metabolic rewiring as a distinct downstream consequence of mutant GTF2I.
Impaired thymic epithelial progenitor differentiation
Mutant GTF2I blocks differentiation of bipotent thymic epithelial progenitors, with the medullary lineage disproportionately affected. The resulting epithelium is dominated by an immature, cortex-like signature and supports reduced thymopoietic activity. This is the mechanistic bridge between the GTF2I oncogenic axis and the medulla-poor architecture that underlies the tolerance defects downstream.
epithelial cell of thymus CL:0002293 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves epithelial cell of thymus (CL:0002293). CL:0002293 is a cell type from the Cell Ontology. medullary thymic epithelial cell CL:0002365 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves medullary thymic epithelial cell (CL:0002365). CL:0002365 is a cell type from the Cell Ontology. cortical thymic epithelial cell CL:0002364 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves cortical thymic epithelial cell (CL:0002364). CL:0002364 is a cell type from the Cell Ontology.
GTF2I hgnc:4659 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves abnormal GTF2I (hgnc:4659). hgnc:4659 is a gene from the HUGO Gene Nomenclature Committee. ⚠ ABNORMAL
thymus UBERON:0002370 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in thymus (UBERON:0002370). UBERON:0002370 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Central tolerance failure in the thymic microenvironment A medulla-poor, cortex-like epithelium lacks the compartment in which negative selection is normally enforced.
Show evidence (2 references)
PMID:36175547 SUPPORT Model Organism
"Co-dominant expression of wild-type and mutated forms of Gtf2i in the mouse thymic epithelium is associated with aberrant thymic architecture and reduced thymopoietic activity."
In vivo modelling of the human driver mutation supports aberrant thymic epithelial architecture and reduced thymopoiesis as a direct consequence.
PMID:36175547 SUPPORT Model Organism
"The resulting gene expression signature is dominated by that of immature cortex-like thymic epithelial cells."
The cortex-like, medulla-poor epithelial signature is the molecular counterpart of the cortex-dominant thymoma architecture seen in patients.
Reduced MHC class II antigen presentation
Many thymomas, especially type A and AB tumors, show reduced MHC class II gene expression, weakening intrathymic antigen presentation.
epithelial cell of thymus CL:0002293 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves epithelial cell of thymus (CL:0002293). CL:0002293 is a cell type from the Cell Ontology.
antigen processing and presentation of peptide antigen via MHC class II GO:0002495 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased antigen processing and presentation of peptide antigen via MHC class II (GO:0002495). GO:0002495 is a biological process from the Gene Ontology. ↓ DECREASED
thymus UBERON:0002370 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in thymus (UBERON:0002370). UBERON:0002370 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Central tolerance failure in the thymic microenvironment Poor self-antigen presentation impairs thymic selection.
Show evidence (1 reference)
PMID:18567864 SUPPORT Human Clinical
"We report here that a) expression levels of class II major histocompatibility complex (MHCII) genes are variably decreased in thymomas, most prominently in histological WHO types A and AB;"
Human thymoma tissue analysis supports reduced MHC class II expression as an atomic mechanism in A/AB thymoma.
AIRE loss in thymic epithelial cells
AIRE expression is absent from most thymomas, reducing tissue-restricted self-antigen display in the thymic epithelial compartment.
medullary thymic epithelial cell CL:0002365 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves medullary thymic epithelial cell (CL:0002365). CL:0002365 is a cell type from the Cell Ontology.
AIRE hgnc:360 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves abnormal AIRE (hgnc:360). hgnc:360 is a gene from the HUGO Gene Nomenclature Committee. ⚠ ABNORMAL
T cell differentiation in thymus GO:0033077 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal T cell differentiation in thymus (GO:0033077). GO:0033077 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Downstream
Central tolerance failure in the thymic microenvironment Loss of AIRE reduces self-antigen-guided thymocyte deletion.
Show evidence (1 reference)
PMID:18567864 SUPPORT Human Clinical
"Recently, we also found that expression of the autoimmune regulator (AIRE) gene is absent from approximately 95% of thymomas."
Human thymoma profiling supports AIRE loss as a distinct central-tolerance defect in thymoma.
Central tolerance failure in the thymic microenvironment
The cortex-dominant, medulla-poor thymoma microenvironment generates autoreactive effector T cells and underproduces regulatory T cells, allowing self-reactive T-cell escape.
epithelial cell of thymus CL:0002293 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves epithelial cell of thymus (CL:0002293). CL:0002293 is a cell type from the Cell Ontology. medullary thymic epithelial cell CL:0002365 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves medullary thymic epithelial cell (CL:0002365). CL:0002365 is a cell type from the Cell Ontology. regulatory T cell CL:0000815 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves regulatory T cell (CL:0000815). CL:0000815 is a cell type from the Cell Ontology.
T cell differentiation in thymus GO:0033077 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal T cell differentiation in thymus (GO:0033077). GO:0033077 is a biological process from the Gene Ontology. ⚠ ABNORMAL
thymus UBERON:0002370 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in thymus (UBERON:0002370). UBERON:0002370 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Neuromuscular autoantigen-expressing medullary epithelial niche Residual medullary-like niches can concentrate MG-relevant antigens.
Myasthenia gravis Autoreactive T-cell escape supports pathogenic neuromuscular autoimmunity.
Pure red cell aplasia Immune dysregulation can suppress erythroid precursors.
Good syndrome Immune dysregulation can coexist with thymoma-associated immunodeficiency.
Checkpoint-blockade-unmasked immune-related toxicity A pre-existing tolerance defect lowers the threshold for severe autoimmune toxicity when PD-1/PD-L1 checkpoints are pharmacologically removed.
Show evidence (2 references)
PMID:41098393 SUPPORT Other
"Since thymomas are mainly composed of the cortex, with few medullae, MG may be caused by immature thymoma-derived T cells that fail to undergo negative selection and have not yet acquired sufficient self-tolerance."
Transcriptomic and spatial analyses support negative-selection failure as a central mechanism linking thymoma to autoimmunity.
PMID:18567864 SUPPORT Human Clinical
"Generation of autoreactive CD4(+) effector T cells and defective production of regulatory CD4(+) T cells inside thymomas contribute to the development of myasthenia gravis (MG) in >90% of MG(+) thymomas."
Human thymoma studies support autoreactive effector-T-cell generation and deficient Treg production as distinct components of tolerance failure.
Neuromuscular autoantigen-expressing medullary epithelial niche
Myasthenia gravis-associated thymomas contain neuromuscular antigen-expressing medullary thymic epithelial populations that organize a local immune niche.
medullary thymic epithelial cell CL:0002365 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves medullary thymic epithelial cell (CL:0002365). CL:0002365 is a cell type from the Cell Ontology.
Downstream
Myasthenia gravis Local neuromuscular autoantigen presentation helps focus MG autoimmunity.
Show evidence (2 references)
PMID:41098393 SUPPORT Computational
"By analyzing bulk RNA-sequencing (RNA-seq) and single-cell RNA-seq (scRNA-seq) data from thymomas, we identified neuromuscular medullary thymic epithelial cells (nmTECs) as neuromuscular antigen-expressing cell populations."
Computational analysis of human thymoma transcriptomes supports a specialized neuromuscular autoantigen niche relevant to thymoma-associated MG.
PMID:41098393 SUPPORT Computational
"We observed spatial nmTEC colocalization and an immune niche, inferring an interaction and suggesting a pathological role of nmTECs in MG."
Spatial transcriptomic inference supports a local immune niche downstream of thymoma-associated thymic dysarchitecture.
PD-L1 Mediated Adaptive Immune Resistance
Thymoma tumour cells upregulate PD-L1 (CD274), engaging PD-1 on infiltrating effector T cells and suppressing anti-tumour cytotoxicity. Expression is not uniform across the histologic axis: it is high specifically in the lymphocyte-rich cortical types B2 and B3, which is the molecular rationale for offering checkpoint blockade in those subtypes. This node is the tumour-immune-evasion arm of the entry and is mechanistically separate from the central-tolerance arm, even though both converge on checkpoint-inhibitor therapy - one as the reason to give it, the other as the reason it is dangerous in thymoma.
epithelial cell of thymus CL:0002293 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves epithelial cell of thymus (CL:0002293). CL:0002293 is a cell type from the Cell Ontology.
negative regulation of T cell mediated immunity GO:0002710 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased negative regulation of T cell mediated immunity (GO:0002710). GO:0002710 is a biological process from the Gene Ontology. ↑ INCREASED
thymus UBERON:0002370 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in thymus (UBERON:0002370). UBERON:0002370 is an anatomical location from the Uberon multi-species anatomy ontology.
Show evidence (2 references)
PMID:34568003 SUPPORT Human Clinical
"We found high expression of CD274 (PD-L1) in B2 and B3 thymoma samples, and validated its expression using immunohistochemistry (IHC)."
Transcriptomic detection confirmed at the protein level by IHC establishes PD-L1 upregulation in specific thymoma histotypes.
PMID:34568003 SUPPORT Human Clinical
"The high expression of PD-L1 in B2 and B3 thymomas support the potential application of immunotherapy on certain thymoma subtypes."
The authors draw the therapeutic inference directly, which is what makes this node the treatment target rather than merely a descriptive finding.
✶

Histopathology

1
Thymoma OBLIGATE
Thymic epithelial neoplasm composed of neoplastic epithelial cells admixed with variable numbers of non-neoplastic immature T lymphocytes.
Show evidence (1 reference)
PMID:20207296 SUPPORT Other
"Epithelial tumours of the thymus include thymomas, thymic carcinomas and neuro-endocrine tumours."
Review abstract supports thymoma as a thymic epithelial neoplasm.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Thymoma 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

6
Blood 2
Pure red cell aplasia OCCASIONAL HP:0012410 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is pure red cell aplasia (HP:0012410). HP:0012410 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40983285 SUPPORT Other
"Myasthenia gravis is the most common, followed by less frequent but notable conditions including pure red cell aplasia, Good's syndrome, and various neurologic, dermatologic, and systemic autoimmune disorders."
Contemporary review abstract supports pure red cell aplasia as a recurring thymoma-associated autoimmune phenotype.
Hypogammaglobulinemia Decreased circulating immunoglobulin concentration HP:0004313 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Decreased circulating immunoglobulin concentration (HP:0004313). HP:0004313 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:37729389 SUPPORT Other
"Good's syndrome, an infrequent adult-onset immunodeficiency is characterized by the triad of thymoma, hypogammaglobulinemia, and increased susceptibility to recurrent infections."
Hypogammaglobulinemia is one of the three defining components of the thymoma-associated Good syndrome triad.
PMID:39180607 SUPPORT Human Clinical
"Regular immunoglobulin monitoring in thymoma patients is essential for early GS diagnosis."
Supports low immunoglobulin as the actionable, monitorable laboratory phenotype in thymoma patients.
Immune 1
Recurrent infections OCCASIONAL HP:0002719 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Recurrent infections (HP:0002719). HP:0002719 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39180607 SUPPORT Human Clinical
"Good syndrome (GS), a rare acquired immunodeficiency disorder characterized by thymoma and hypogammaglobulinemia, predisposes individuals to recurrent infections."
Human clinical review data supports recurrent infections as a common downstream phenotype of thymoma-associated Good syndrome.
Respiratory 1
Anterior mediastinal mass OBLIGATE HP:0033827 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is anterior mediastinal mass (HP:0033827). HP:0033827 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37761349 SUPPORT Other
"Thymomas are considered one of the most prevalent types of mediastinal epithelial tumors, which frequently develop in the anterior mediastinum."
Review abstract supports the characteristic anterior mediastinal presentation of thymoma.
Other 2
Myasthenia gravis FREQUENT MONDO:0009688 Mondo Disease Ontology (MONDO) Relation: this clinical feature is this phenotype This clinical feature is myasthenia gravis (MONDO:0009688). MONDO:0009688 is a phenotype from the Mondo Disease Ontology.
Show evidence (2 references)
PMID:20207296 SUPPORT Other
"Thymomas, in particular, can be associated to auto-immune disorders, among which predominates myasthenia gravis."
Review abstract identifies myasthenia gravis as the leading autoimmune phenotype associated with thymoma.
PMID:25521402 SUPPORT Human Clinical
"In total, 38% of patients with thymoma had myasthenia gravis compared with less than or equal to 5% for thymic carcinoma and thymic"
Quantitative support for the FREQUENT band specifically: 38% in the ITMIG international database of 6097 thymic malignancy cases falls in the 30-79% HPO frequency range. The contrast with thymic carcinoma also confirms that the association is thymoma-specific rather than generic to thymic tumors.
Good syndrome OCCASIONAL MONDO:0015696 Mondo Disease Ontology (MONDO) Relation: this clinical feature is this phenotype This clinical feature is Good syndrome (MONDO:0015696). MONDO:0015696 is a phenotype from the Mondo Disease Ontology.
Show evidence (1 reference)
PMID:39180607 SUPPORT Human Clinical
"Good syndrome (GS), a rare acquired immunodeficiency disorder characterized by thymoma and hypogammaglobulinemia, predisposes individuals to recurrent infections."
Human case-review evidence supports Good syndrome as a bona fide thymoma-associated immunodeficiency phenotype.
🧬

Genetic Associations

2
GTF2I mutation (Recurrent somatic driver mutation)
Gene: GTF2I hgnc:4659 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is GTF2I (hgnc:4659). hgnc:4659 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (3 references)
PMID:24974848 SUPPORT Human Clinical
"In a series of 274 TETs, we detected the GTF2I mutation in 82% of type A and 74% of type AB thymomas but rarely in the aggressive subtypes, where recurrent mutations of known cancer genes have been identified."
Human tumor profiling establishes GTF2I as the dominant recurrent somatic alteration in indolent thymoma histotypes.
PMID:41405018 SUPPORT Human Clinical
"GTF2I mutations were prevalent in type A and AB thymomas, in Stage I-II tumors, and in patients without myasthenia gravis."
Prospective sequencing confirms the type A/AB enrichment and adds two further associations: early stage, and - notably - the ABSENCE of myasthenia gravis. The inverse relationship between the GTF2I-mutant molecular facet and the autoimmune phenotype is what keeps the oncogenic and tolerance-failure axes of this entry separate rather than sequential.
PMID:41405018 SUPPORT Human Clinical
"GTF2I mutations were the most common, being present in 41% of patients."
Independent prospective cohort estimate of GTF2I mutation frequency across unselected thymic epithelial tumours.
HRAS mutation (Recurrent somatic mutation)
Gene: HRAS hgnc:5173 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is HRAS (hgnc:5173). hgnc:5173 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (1 reference)
PMID:38338833 SUPPORT Other
"Thymomas exhibit a limited mutational load, with prevalent GTF2I and HRAS mutations."
Review synthesis supports HRAS as one of the recurrent mutations in thymoma despite overall low tumor mutational burden.
💊

Medical Actions

5
Thymectomy
Action: thymectomyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is thymectomy (NCIT:C29894). NCIT:C29894 is a clinical intervention from the NCI Thesaurus. Ontology label: Thymectomy NCIT:C29894
Complete surgical resection is the central treatment for localized thymoma and can improve coexisting myasthenia gravis.
Show evidence (2 references)
PMID:20207296 SUPPORT Other
"The initial treatment, as well as that of the recurrence, is based mainly on a complete resection."
Review abstract supports complete surgical resection as the core treatment of thymoma.
PMID:40983285 SUPPORT Other
"Surgical intervention through thymectomy remains a cornerstone of treatment, particularly for myasthenia gravis, where it can lead to considerable symptomatic improvement."
Review abstract supports thymectomy as both oncologic and autoimmune disease management in thymoma.
Postoperative radiotherapy
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. Ontology label: Radiation Therapy NCIT:C15313
Platform: Radiotherapy
Adjuvant radiotherapy is used for invasive thymoma, incomplete resection, or aggressive histologic subtypes.
Show evidence (1 reference)
PMID:20207296 SUPPORT Other
"Postoperative radiotherapy is systematically added to the treatment of invasive tumours and/or to those with an aggressive histological subtype."
Review abstract supports adjuvant radiotherapy for invasive or more aggressive thymoma facets.
Platinum-anthracycline chemotherapy
Action: chemotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is chemotherapy (NCIT:C15632). NCIT:C15632 is a clinical intervention from the NCI Thesaurus. Ontology label: Chemotherapy NCIT:C15632
Agent: cisplatin CHEBI:27899 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses cisplatin (CHEBI:27899). CHEBI:27899 is a therapeutic agent from Chemical Entities of Biological Interest. doxorubicin CHEBI:28748 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses doxorubicin (CHEBI:28748). CHEBI:28748 is a therapeutic agent from Chemical Entities of Biological Interest.
Cisplatin-based multi-agent chemotherapy is used for unresectable, metastatic, or recurrent thymoma.
Show evidence (1 reference)
PMID:20207296 SUPPORT Other
"Inoperable or metastatic tumours require a cisplatine and anthracyclin-based chemotherapy, followed by radical surgery and/or radiotherapy."
Review abstract supports platinum-anthracycline chemotherapy as the standard systemic therapy for unresectable or metastatic thymoma.
Systemic immunosuppression
Action: immune suppressant agent therapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is immune suppressant agent therapy, annotated with Immunosuppressive Therapy (NCIT:C15261). NCIT:C15261 is a clinical intervention from the NCI Thesaurus. Ontology label: Immunosuppressive Therapy NCIT:C15261
Immunosuppressive therapy is often needed when thymoma-associated autoimmunity persists or emerges after thymectomy.
Show evidence (1 reference)
PMID:40983285 SUPPORT Other
"However, autoimmune conditions may persist or even develop after thymectomy, necessitating disease-specific approaches with systemic immunosuppression."
Review abstract supports systemic immunosuppression for thymoma-associated autoimmune complications that are not fully controlled by surgery.
Immune Checkpoint Blockade
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: pembrolizumab NCIT:C106432 NCI Thesaurus (NCIT) Relation: this treatment uses this therapeutic agent This treatment uses pembrolizumab (NCIT:C106432). NCIT:C106432 is a therapeutic agent from the NCI Thesaurus.
Platform: Monoclonal antibody
PD-1/PD-L1 blockade (pembrolizumab, nivolumab, avelumab, atezolizumab) has activity in pretreated advanced thymic epithelial tumours but is used with caution in thymoma specifically. SAFETY CAVEAT: grade 3-5 immune-related adverse events occurred in 58.3% of thymoma patients versus 17.1% of thymic carcinoma patients in a meta-analysis of six phase I/II trials, so the benefit-risk balance is far less favourable in thymoma than in thymic carcinoma and close monitoring is required. The excess toxicity is modelled in this entry as the "Checkpoint-blockade-unmasked immune-related toxicity" pathophysiology node, downstream of the same central-tolerance failure that drives the spontaneous paraneoplastic syndromes.
Mechanism Target:
INHIBITS PD-L1 Mediated Adaptive Immune Resistance — PD-1/PD-L1 blockade releases the inhibitory signal that thymoma cells impose on infiltrating effector T cells, which is the anti-tumour rationale for the drug. Note that the toxicity this therapy causes is modelled on a separate node reached from the central-tolerance arm, not from here.
Show evidence (1 reference)
PMID:34568003 SUPPORT Human Clinical
"The high expression of PD-L1 in B2 and B3 thymomas support the potential application of immunotherapy on certain thymoma subtypes."
Ties the drug to the specific PD-L1 node it acts on, and to the histotypes in which that node is active.
Show evidence (2 references)
PMID:36592506 SUPPORT Human Clinical
"The overall response rate to ICB was 18.4%"
Establishes measurable but modest activity. Marked PARTIAL because the pooled cohort was 77% thymic carcinoma and only 23% thymoma, so the response estimate is not thymoma-specific.
PMID:36592506 SUPPORT Human Clinical
"our results suggest ICB as a potential strategy in patients with pretreated TET, mainly among patients with thymic carcinoma. Close monitoring is strongly advised to detect severe immune-toxicity."
The authors' own conclusion steers checkpoint blockade toward thymic carcinoma rather than thymoma, which is why this treatment is recorded here with an explicit safety caveat rather than as standard therapy.
🔬

Biochemical Markers

1
Anti-titin antibody positivity (present)
Context: Measured in myasthenia gravis patients. The FREQUENT band is conditioned on the thymectomized MG cohort in which it was established (56 of 70 thymoma patients), NOT on unselected thymoma patients, in whom the rate is not established by this source.
Show evidence (2 references)
PMID:11405802 SUPPORT Human Clinical
"anti-titin antibodies were present in most patients with thymoma"
Supports the FREQUENT band for anti-titin positivity among thymoma patients; the underlying counts are 56/70 thymoma versus 17/165 thymic atrophy or hyperplasia.
PMID:11405802 SUPPORT Human Clinical
"Anti-titin antibodies are a sensitive marker of thymoma associated with MG in patients 60 years and younger, justifying the insistent search for a thymoma in MG patients of this age group who have these antibodies."
States the age-conditioned clinical use of the marker, which is how it functions in thymoma workup.
📈

Progression

3
Adult-onset presentation
Age: sixth to seventh decade
Thymoma is an adult-onset tumor; registry series place the mean age at diagnosis near 60 years in both the US and Germany, with a male-to-female ratio close to 1.
Show evidence (1 reference)
PMID:38264756 SUPPORT Human Clinical
"The male-to-female ratio was 1:1.09/1.03, and the mean age 59.48 ± 14.89/61.33 ± 13.94."
Registry data establish the adult, near-sixth-decade onset and the approximately equal sex ratio.
Locally advanced and disseminated disease
Progression is captured clinically by Masaoka-Koga stage. Advanced (stage III/IV) disease is an independent predictor of worse overall survival after resection.
Show evidence (1 reference)
PMID:42260490 SUPPORT Human Clinical
"Advanced Masaoka-Koga stage (III/IV) independently predicted worse OS"
Multivariable analysis of a surgical thymoma cohort supports Masaoka-Koga stage as an independent prognostic axis of disease progression.
Post-resection surveillance
Primary tumor size is an independent prognostic factor in resected thymoma (but not in thymic carcinoma), supporting size-aware long-term follow-up.
Show evidence (1 reference)
PMID:39730963 SUPPORT Human Clinical
"Tumor size in thymoma, but not in thymic carcinoma, was an important prognostic factor in the U.S."
NCDB analysis supports tumor size as a thymoma-specific prognostic factor after resection.
📊

Prevalence

2
United States
Annual Incidence 0.22 per 100,000 1–9 per 1,000,000 per year
SEER-based US annual incidence of 2.2 per million inhabitants (equivalently 0.22 per 100,000), 1999-2019. The companion German (ZfKD) estimate over the same period was 2.64 per million.
Show evidence (1 reference)
PMID:38264756 SUPPORT Human Clinical
"The overall annual incidence of thymoma was 2.2/2.64 (US/GER) per million inhabitants and for thymic carcinomas 0.48/0.42."
Registry-derived annual incidence for thymoma in two national populations.
Germany
Annual Incidence 0.264 per 100,000 1–9 per 1,000,000 per year
ZfKD (German national cancer registry) annual incidence of 2.64 per million inhabitants, 1999-2019.
Show evidence (1 reference)
PMID:38264756 SUPPORT Human Clinical
"The overall annual incidence of thymoma was 2.2/2.64 (US/GER) per million inhabitants and for thymic carcinomas 0.48/0.42."
The same registry comparison gives the German incidence figure.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Thymoma:

Lymphoma MONDO:0004021
Overlapping Features The main alternative diagnosis for an anterior mediastinal mass in adults, and the one whose management diverges most sharply, since lymphoma is treated medically rather than by upfront resection.
Distinguishing Features
  • Second most common anterior mediastinal tumour in adults after thymic epithelial tumours, and far more prominent than thymic tumours in patients under 20 years.
  • Lacks the paraneoplastic autoimmune syndromes (myasthenia gravis, pure red cell aplasia, Good syndrome) that characterise thymoma.
  • Lacks the organotypic thymic architecture and the admixed immature T lymphocytes seen histologically in thymoma.
  • Requires tissue biopsy and medical therapy rather than upfront surgical resection, so misclassification changes management directly.
Show evidence (1 reference)
PMID:38264756 SUPPORT Human Clinical
"Among patients aged ≥20 years, TETs accounted for the most prevalent anterior mediastinal tumors (US/GER: 63%/64%), followed by lymphomas (14%/8%)."
Quantifies lymphoma as the leading non-thymic alternative for an adult anterior mediastinal mass.
Mediastinal germ cell tumor Not Yet Curated MONDO:0021067
Overlapping Features The dominant anterior mediastinal tumour of children and young adults, in whom thymoma is rare.
Distinguishing Features
  • Predominates in patients under 20 years, an age band in which thymic epithelial tumours are distinctly uncommon.
  • Identifiable by serum tumour markers rather than by the autoimmune phenomenology that flags thymoma.
Show evidence (1 reference)
PMID:38264756 SUPPORT Human Clinical
"For patients <20 years, predominant tumors included germ cell tumors (42%/14%), lymphomas (38%/53%), and TETs (10%/27%)."
Establishes the age-dependent inversion that makes germ cell tumour the leading differential in young patients.
📊

Related Datasets

3
Altered thymopoiesis in thymoma is associated with defects in negative selection machinery and decreased Treg abundance geo:GSE284479
Thymomas are rare thymic epithelial tumors harboring a high but variable proportion of lymphocytes without obvious function. Auto-immunity is present in one third of patients at diagnosis. Herein, we performed a phenotypic, scRNAseq, and spatial analysis of both the T cells and tumoral cells. All stages of T cell development -from immature to mature- were present in the tumor suggesting active thymopoiesis in thymoma. However, multiple approaches suggest a maturation blockade at the DN-DP stages. In the mature T cell compartment, the frequency of Tregs was strongly decreased.
human MULTI OMICS n=53
PMID:41143696
Identified by GEO DataSets index search for Thymoma (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.
RNA-Seq analysis of human MEN1-associated thymic carcinoid and thymoma compared to normal thymus geo:GSE177522
RNA-Sequencing was performed on rRNA-depleted RNA samples that were isolated from formalin fixed paraffin embedded (FFPE) tissue sections of human normal thymus and human thymic tumors of patients with multiple endocrine neoplasia type 1 (MEN1) syndrome.
human BULK RNA SEQ n=19
PMID:34515662
Identified by GEO DataSets index search for Thymoma (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.
DNA-Methylation Analysis as a Tool for Thymoma Classification geo:GSE218549
Thymomas are malignant thymic epithelial tumors that are difficult to diagnose due to their rarity and complex diagnostic criteria. They represent a morphologically heterogeneous class of tumors mainly defined by “organo-typical” architectural features and cellular composition. The diagnosis of thymoma is burdened with a high inter-observer variability and with the problem that some type-specific morphological alterations are rather a continuum than clear-cut. Methylation pattern-based classification may help to increase diagnostic precision, particularly in borderline cases.
human METHYLATION n=122
PMID:36497358
Identified by GEO DataSets index search for Thymoma (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.
{ }

Source YAML

click to show 
name: Thymoma
creation_date: '2026-03-16T06:37:22Z'
description: >-
  Thymoma is a thymic epithelial tumor of the anterior mediastinum that is best
  modeled in dismech as one disease-level mechanism graph with histologic and
  invasion-status subtype facets rather than separate disease pages. Thymomas
  have a lower mutational burden than thymic carcinoma, are enriched for GTF2I
  mutations in WHO type A and AB tumors, and uniquely perturb thymic selection
  programs so that impaired central tolerance drives autoimmune syndromes such
  as myasthenia gravis, pure red cell aplasia, and Good syndrome. That same
  tolerance defect makes thymoma an outlier for checkpoint-inhibitor toxicity:
  severe immune-related adverse events are more than three times as frequent in
  thymoma as in thymic carcinoma treated with the same agents, so the toxicity
  is modeled here as a therapy-unmasked branch of the tolerance-failure chain
  rather than as an unrelated drug side effect.
category: Neoplastic
categories:
- Thymic epithelial tumor
- Mediastinal neoplasm
- Thoracic cancer
parents:
- thymic epithelial neoplasm
disease_term:
  preferred_term: thymoma
  term:
    id: MONDO:0006456
    label: thymoma
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0006456
      label: thymoma
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
  ncit_mappings:
  - term:
      id: NCIT:C3411
      label: Thymoma
    mapping_predicate: skos:exactMatch
    mapping_source: NCIT
notes: >-
  Following the cancer curation guidance from issue 1198, this entry treats
  thymoma as the disease-level mechanism-graph unit. WHO histotypes and
  invasion status are represented as flat subtype facets grounded to NCIT,
  rather than as separate dismech disease pages.
classifications:
  harrisons_chapter:
  - classification_value: ONCOLOGY_HEMATOLOGY
    evidence:
    - reference: PMID:38264756
      reference_title: "Epidemiology of thymomas and thymic carcinomas in the United States and Germany, 1999-2019."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Patients aged 0-19 (n=478) and ≥20 years (n=17,459) diagnosed with
        malignant tumors of the anterior mediastinum were identified from the
        Surveillance, Epidemiology, and End Results registry (SEER)
      explanation: >-
        Thymoma is registered and analysed as a malignant neoplasm in national
        cancer registries, supporting an oncology classification.
  - classification_value: IMMUNE_RHEUMATOLOGIC
    evidence:
    - reference: PMID:40983285
      reference_title: "Management of Autoimmune Conditions Associated With Thymic Epithelial Tumors."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Thymic epithelial tumors are associated with diverse autoimmune
        manifestations, with 30% to 50% of patients developing at least one
        autoimmune condition.
      explanation: >-
        A third to a half of patients develop autoimmune disease, so thymoma
        also belongs to the immune/rheumatologic axis rather than oncology alone.
prevalence:
- population: United States
  measure_type: ANNUAL_INCIDENCE
  prevalence_class: BAND_1_9_PER_1000000
  rate_per_100000: 0.22
  notes: >-
    SEER-based US annual incidence of 2.2 per million inhabitants (equivalently
    0.22 per 100,000), 1999-2019. The companion German (ZfKD) estimate over the
    same period was 2.64 per million.
  evidence:
  - reference: PMID:38264756
    reference_title: "Epidemiology of thymomas and thymic carcinomas in the United States and Germany, 1999-2019."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The overall annual incidence of thymoma was 2.2/2.64 (US/GER) per million
      inhabitants and for thymic carcinomas 0.48/0.42.
    explanation: >-
      Registry-derived annual incidence for thymoma in two national populations.
- population: Germany
  measure_type: ANNUAL_INCIDENCE
  prevalence_class: BAND_1_9_PER_1000000
  rate_per_100000: 0.264
  notes: >-
    ZfKD (German national cancer registry) annual incidence of 2.64 per million
    inhabitants, 1999-2019.
  evidence:
  - reference: PMID:38264756
    reference_title: "Epidemiology of thymomas and thymic carcinomas in the United States and Germany, 1999-2019."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The overall annual incidence of thymoma was 2.2/2.64 (US/GER) per million
      inhabitants and for thymic carcinomas 0.48/0.42.
    explanation: >-
      The same registry comparison gives the German incidence figure.
progression:
- phase: Adult-onset presentation
  age_range: sixth to seventh decade
  notes: >-
    Thymoma is an adult-onset tumor; registry series place the mean age at
    diagnosis near 60 years in both the US and Germany, with a male-to-female
    ratio close to 1.
  evidence:
  - reference: PMID:38264756
    reference_title: "Epidemiology of thymomas and thymic carcinomas in the United States and Germany, 1999-2019."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The male-to-female ratio was 1:1.09/1.03, and the mean age 59.48 ± 14.89/61.33 ± 13.94.
    explanation: >-
      Registry data establish the adult, near-sixth-decade onset and the
      approximately equal sex ratio.
- phase: Locally advanced and disseminated disease
  notes: >-
    Progression is captured clinically by Masaoka-Koga stage. Advanced
    (stage III/IV) disease is an independent predictor of worse overall
    survival after resection.
  evidence:
  - reference: PMID:42260490
    reference_title: "Comparative effectiveness of video-assisted thoracoscopic surgery versus open thymectomy for thymoma: a propensity score-matched analysis of 317 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Advanced Masaoka-Koga stage (III/IV) independently predicted worse OS
    explanation: >-
      Multivariable analysis of a surgical thymoma cohort supports Masaoka-Koga
      stage as an independent prognostic axis of disease progression.
- phase: Post-resection surveillance
  notes: >-
    Primary tumor size is an independent prognostic factor in resected thymoma
    (but not in thymic carcinoma), supporting size-aware long-term follow-up.
  evidence:
  - reference: PMID:39730963
    reference_title: "Prognostic Impact of Primary Tumor Size in Thymic Epithelial Tumor: An NCDB-Based Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Tumor size in thymoma, but not in thymic carcinoma, was an important
      prognostic factor in the U.S.
    explanation: >-
      NCDB analysis supports tumor size as a thymoma-specific prognostic factor
      after resection.
has_subtypes:
- name: Type A thymoma
  classification: histological_pattern
  subtype_term:
    preferred_term: Type A thymoma
    term:
      id: NCIT:C6454
      label: Thymoma Type A
  description: >-
    Spindle-cell thymoma with relatively indolent clinical behavior and marked
    enrichment for GTF2I mutation.
  evidence:
  - reference: PMID:24974848
    reference_title: "A specific missense mutation in GTF2I occurs at high frequency in thymic epithelial tumors."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We analyzed 28 thymic epithelial tumors (TETs) using next-generation
      sequencing and identified a missense mutation (chromosome 7
      c.74146970T>A) in GTF2I at high frequency in type A thymomas, a
      relatively indolent subtype.
    explanation: >-
      Human tumor sequencing links WHO type A thymoma to indolent biology and a
      strong GTF2I-mutant state.
- name: Type AB thymoma
  classification: histological_pattern
  subtype_term:
    preferred_term: Type AB thymoma
    term:
      id: NCIT:C6885
      label: Thymoma Type AB
  description: >-
    Mixed spindle-cell and lymphocyte-rich thymoma that shares much of the
    GTF2I-enriched molecular profile of type A thymoma.
  evidence:
  - reference: PMID:24974848
    reference_title: "A specific missense mutation in GTF2I occurs at high frequency in thymic epithelial tumors."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In a series of 274 TETs, we detected the GTF2I mutation in 82% of type A
      and 74% of type AB thymomas but rarely in the aggressive subtypes, where
      recurrent mutations of known cancer genes have been identified.
    explanation: >-
      Large human tumor series supports type AB thymoma as part of the
      GTF2I-enriched, less aggressive facet of thymoma.
- name: Type B1 thymoma
  classification: histological_pattern
  subtype_term:
    preferred_term: Type B1 thymoma
    term:
      id: NCIT:C6887
      label: Thymoma Type B1
  description: >-
    Cortical-like thymoma rich in immature T lymphocytes, generally showing less
    invasion than type B3 thymoma.
  evidence:
  - reference: PMID:15063231
    reference_title: "WHO histologic classification is a prognostic indicator in thymoma."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The frequency of invasion to neighboring organs increased according to
      tumor subtype in the order A (0%), AB (6%), B1 (19%), B2 (25%), B3 (42%),
      and C (89%).
    explanation: >-
      Positions type B1 on the invasion gradient below B2 and B3, supporting its
      intermediate place on the histologic subtype axis.
- name: Type B2 thymoma
  classification: histological_pattern
  subtype_term:
    preferred_term: Type B2 thymoma
    term:
      id: NCIT:C6888
      label: Thymoma Type B2
  description: >-
    Cortical thymoma with numerous lymphocytes and more conspicuous neoplastic
    epithelial cells; often associated with myasthenia gravis. It is the single
    most frequently assigned WHO histotype among thymomas.
  evidence:
  - reference: PMID:25521402
    reference_title: "Development of the international thymic malignancy interest group international database: an unprecedented resource for the study of a rare group of tumors."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      WHO type B2 was the most frequent histologic classification among thymomas,
      whereas squamous was the most common among thymic carcinomas.
    explanation: >-
      The ITMIG international database establishes type B2 as the most common
      thymoma histotype, supporting its prominence on the histologic subtype axis.
- name: Type B3 thymoma
  classification: histological_pattern
  subtype_term:
    preferred_term: Type B3 thymoma
    term:
      id: NCIT:C7997
      label: Thymoma Type B3
  description: >-
    Epithelial-predominant thymoma with higher local invasiveness and worse
    disease-free survival than type A/AB and B1/B2 thymomas.
  evidence:
  - reference: PMID:15063231
    reference_title: "WHO histologic classification is a prognostic indicator in thymoma."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The frequency of invasion to neighboring organs increased according to
      tumor subtype in the order A (0%), AB (6%), B1 (19%), B2 (25%), B3 (42%),
      and C (89%).
    explanation: >-
      Human surgical series supports higher invasive propensity in type B3
      thymoma than in lower-grade WHO thymoma histotypes.
  - reference: PMID:15063231
    reference_title: "WHO histologic classification is a prognostic indicator in thymoma."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The disease-free survival rates were 100% for types A and AB, 83% for
      types B1 and B2, 36% for type B3, and 28% for type C thymoma at 10 years.
    explanation: >-
      Long-term follow-up supports the prognostic distinction of type B3 within
      the thymoma histologic axis.
- name: Encapsulated thymoma
  classification: invasion_status
  subtype_term:
    preferred_term: encapsulated thymoma
    term:
      id: NCIT:C7386
      label: Encapsulated Thymoma
  description: >-
    Organ-confined thymoma without gross invasion, generally corresponding to a
    more resectable and clinically indolent presentation.
  evidence:
  - reference: PMID:15063231
    reference_title: "WHO histologic classification is a prognostic indicator in thymoma."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The frequency of invasion to neighboring organs increased according to
      tumor subtype in the order A (0%), AB (6%), B1 (19%), B2 (25%), B3 (42%),
      and C (89%).
    explanation: >-
      Supports a substantial non-invasive, organ-confined population within
      thymoma (no invasion at all in type A), which is what the encapsulated pole
      of this axis captures. Marked PARTIAL because the series reports invasion
      frequency by histotype rather than encapsulation status directly.
- name: Invasive thymoma
  classification: invasion_status
  subtype_term:
    preferred_term: invasive thymoma
    term:
      id: NCIT:C7904
      label: Invasive Malignant Thymoma
  description: >-
    Thymoma that invades neighboring structures or disseminates intrathoracically
    and more often requires multimodal treatment.
  evidence:
  - reference: PMID:20207296
    reference_title: "[Epithelial tumours of the thymus]."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Their clinical behaviour varies widely, from a relative indolence to the
      potential of lymph node and/or systematic metastases.
    explanation: >-
      Review-level evidence supports an invasion-status facet within thymoma
      that is distinct from WHO histologic subtype.
pathophysiology:
- name: GTF2I-driven thymic epithelial transformation
  biological_scale: CELLULAR
  subtypes:
  - Type A thymoma
  - Type AB thymoma
  description: >-
    Recurrent GTF2I mutation defines a major molecular facet of type A and AB
    thymoma and promotes thymic epithelial proliferation and transformation.
  gene:
    preferred_term: GTF2I
    description: Recurrently mutated thymoma driver, usually p.L424H.
    modifier: ABNORMAL
    term:
      id: hgnc:4659
      label: GTF2I
  cell_types:
  - preferred_term: epithelial cell of thymus
    term:
      id: CL:0002293
      label: epithelial cell of thymus
  biological_processes:
  - preferred_term: cell population proliferation
    modifier: INCREASED
    term:
      id: GO:0008283
      label: cell population proliferation
  locations:
  - preferred_term: thymus
    term:
      id: UBERON:0002370
      label: thymus
  evidence:
  - reference: PMID:24974848
    reference_title: "A specific missense mutation in GTF2I occurs at high frequency in thymic epithelial tumors."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In a series of 274 TETs, we detected the GTF2I mutation in 82% of type A
      and 74% of type AB thymomas but rarely in the aggressive subtypes, where
      recurrent mutations of known cancer genes have been identified.
    explanation: >-
      Human tumor sequencing supports GTF2I mutation as the defining molecular
      driver of the indolent A/AB thymoma facet.
  - reference: PMID:32034314
    reference_title: "Mutant GTF2I induces cell transformation and metabolic alterations in thymic epithelial cells."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Our findings identify GTF2I mutation as a new oncogenic driver that is
      responsible for transformation of thymic epithelial cells.
    explanation: >-
      Cell-based functional evidence directly shows that mutant GTF2I can drive
      thymic epithelial transformation.
  - reference: PMID:36049655
    reference_title: "A Knock-In Mouse Model of Thymoma With the GTF2I L424H Mutation."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We observed that the Gtf2i mutation impairs development of the thymic
      medulla and maturation of medullary thymic epithelial cells in young mice
      and causes tumor formation in the thymus of aged mice.
    explanation: >-
      Conditional knock-in of the human hotspot allele into Foxn1-positive thymic
      epithelium is sufficient to produce thymoma in vivo, raising the
      transformation claim above the in vitro evidence alone.
  - reference: PMID:36049655
    reference_title: "A Knock-In Mouse Model of Thymoma With the GTF2I L424H Mutation."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Results of gene set variation assay analysis revealed that gene signatures
      of cortical thymic epithelial cells and thymic epithelial progenitor cells
      are also enriched in the thymomas of the knock-in mice, which mirrors the
      human counterparts in The Cancer Genome Atlas database.
    explanation: >-
      The murine tumours reproduce the cortical/progenitor transcriptional
      signature of human thymoma, supporting the model's relevance to the human
      transformation programme.
  downstream:
  - target: Metabolic stress survival program
    description: Mutant TFII-I supports stress-adapted growth states.
    evidence:
    - reference: PMID:32034314
      reference_title: "Mutant GTF2I induces cell transformation and metabolic alterations in thymic epithelial cells."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Gtf2i L424H knockin cells exhibited cell transformation, aneuploidy, and
        increase tumor growth and survival under glucose deprivation or DNA
        damage.
      explanation: >-
        Introducing the GTF2I lesion is sufficient to confer the stress-adapted
        survival state, supporting a causal edge from the transformation node to
        the metabolic program.
  - target: Impaired thymic epithelial progenitor differentiation
    description: >-
      Mutant GTF2I skews bipotent thymic epithelial progenitors away from
      medullary differentiation.
    evidence:
    - reference: PMID:36175547
      reference_title: "Human thymoma-associated mutation of the GTF2I transcription factor impairs thymic epithelial progenitor differentiation in mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Phenotypic and molecular characterization of the mutant epithelium
        indicates that medullary differentiation is particularly affected as a
        result of impaired differentiation of bi-potent epithelial progenitors.
      explanation: >-
        A mouse model carrying the human thymoma GTF2I mutation shows that the
        driver lesion causally impairs medullary epithelial differentiation.
- name: Metabolic stress survival program
  biological_scale: CELLULAR
  subtypes:
  - Type A thymoma
  - Type AB thymoma
  description: >-
    Mutant GTF2I rewires glycolytic and stress-response programs, supporting
    tumor growth and survival under nutrient and DNA-damage stress.
  gene:
    preferred_term: GTF2I
    modifier: ABNORMAL
    term:
      id: hgnc:4659
      label: GTF2I
  biological_processes:
  - preferred_term: glycolytic process
    modifier: INCREASED
    term:
      id: GO:0006096
      label: glycolytic process
  evidence:
  - reference: PMID:32034314
    reference_title: "Mutant GTF2I induces cell transformation and metabolic alterations in thymic epithelial cells."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Gtf2i L424H knockin cells exhibited cell transformation, aneuploidy, and
      increase tumor growth and survival under glucose deprivation or DNA
      damage.
    explanation: >-
      In vitro knock-in experiments support a stress-survival program downstream
      of mutant GTF2I.
  - reference: PMID:32034314
    reference_title: "Mutant GTF2I induces cell transformation and metabolic alterations in thymic epithelial cells."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Gtf2i mutation also increased the expression of several glycolytic
      enzymes, cyclooxygenase-2, and caused modifications of lipid metabolism.
    explanation: >-
      The same in vitro study supports metabolic rewiring as a distinct
      downstream consequence of mutant GTF2I.
- name: Impaired thymic epithelial progenitor differentiation
  biological_scale: CELLULAR
  description: >-
    Mutant GTF2I blocks differentiation of bipotent thymic epithelial
    progenitors, with the medullary lineage disproportionately affected. The
    resulting epithelium is dominated by an immature, cortex-like signature and
    supports reduced thymopoietic activity. This is the mechanistic bridge
    between the GTF2I oncogenic axis and the medulla-poor architecture that
    underlies the tolerance defects downstream.
  gene:
    preferred_term: GTF2I
    modifier: ABNORMAL
    term:
      id: hgnc:4659
      label: GTF2I
  cell_types:
  - preferred_term: epithelial cell of thymus
    term:
      id: CL:0002293
      label: epithelial cell of thymus
  - preferred_term: medullary thymic epithelial cell
    term:
      id: CL:0002365
      label: medullary thymic epithelial cell
  - preferred_term: cortical thymic epithelial cell
    term:
      id: CL:0002364
      label: cortical thymic epithelial cell
  locations:
  - preferred_term: thymus
    term:
      id: UBERON:0002370
      label: thymus
  evidence:
  - reference: PMID:36175547
    reference_title: "Human thymoma-associated mutation of the GTF2I transcription factor impairs thymic epithelial progenitor differentiation in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Co-dominant expression of wild-type and mutated forms of Gtf2i in the mouse
      thymic epithelium is associated with aberrant thymic architecture and
      reduced thymopoietic activity.
    explanation: >-
      In vivo modelling of the human driver mutation supports aberrant thymic
      epithelial architecture and reduced thymopoiesis as a direct consequence.
  - reference: PMID:36175547
    reference_title: "Human thymoma-associated mutation of the GTF2I transcription factor impairs thymic epithelial progenitor differentiation in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The resulting gene expression signature is dominated by that of immature
      cortex-like thymic epithelial cells.
    explanation: >-
      The cortex-like, medulla-poor epithelial signature is the molecular
      counterpart of the cortex-dominant thymoma architecture seen in patients.
  downstream:
  - target: Central tolerance failure in the thymic microenvironment
    description: >-
      A medulla-poor, cortex-like epithelium lacks the compartment in which
      negative selection is normally enforced.
    evidence:
    - reference: PMID:18401674
      reference_title: "Immunological function of thymoma and pathogenesis of paraneoplastic myasthenia gravis."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        this might imply that thymoma lacks the functional medulla where
        professional antigen-presenting cells are engaged in negative selection.
      explanation: >-
        Links the cortical-epithelial character of thymoma to absence of the
        medullary compartment that performs negative selection.
- name: Reduced MHC class II antigen presentation
  biological_scale: CELLULAR
  subtypes:
  - Type A thymoma
  - Type AB thymoma
  description: >-
    Many thymomas, especially type A and AB tumors, show reduced MHC class II
    gene expression, weakening intrathymic antigen presentation.
  cell_types:
  - preferred_term: epithelial cell of thymus
    term:
      id: CL:0002293
      label: epithelial cell of thymus
  biological_processes:
  - preferred_term: antigen processing and presentation of peptide antigen via MHC class II
    modifier: DECREASED
    term:
      id: GO:0002495
      label: antigen processing and presentation of peptide antigen via MHC class II
  locations:
  - preferred_term: thymus
    term:
      id: UBERON:0002370
      label: thymus
  evidence:
  - reference: PMID:18567864
    reference_title: "Common cellular and diverse genetic basis of thymoma-associated myasthenia gravis: role of MHC class II and AIRE genes and genetic polymorphisms."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We report here that a) expression levels of class II major
      histocompatibility complex (MHCII) genes are variably decreased in
      thymomas, most prominently in histological WHO types A and AB;
    explanation: >-
      Human thymoma tissue analysis supports reduced MHC class II expression as
      an atomic mechanism in A/AB thymoma.
  downstream:
  - target: Central tolerance failure in the thymic microenvironment
    description: Poor self-antigen presentation impairs thymic selection.
    evidence:
    - reference: PMID:18401674
      reference_title: "Immunological function of thymoma and pathogenesis of paraneoplastic myasthenia gravis."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        The impaired expression of HLA-DR molecules in neoplastic epithelial
        cells of thymomas possibly affects positive selection of
        CD4(+)CD8(-) single-positive T cells and may result in alteration of its
        repertoire.
      explanation: >-
        Reduced class II (HLA-DR) display on thymoma epithelium is proposed to
        distort thymic selection and the resulting T-cell repertoire.
- name: AIRE loss in thymic epithelial cells
  biological_scale: MOLECULAR
  description: >-
    AIRE expression is absent from most thymomas, reducing tissue-restricted
    self-antigen display in the thymic epithelial compartment.
  gene:
    preferred_term: AIRE
    description: Autoimmune regulator required for central tolerance.
    modifier: ABNORMAL
    term:
      id: hgnc:360
      label: AIRE
  cell_types:
  - preferred_term: medullary thymic epithelial cell
    term:
      id: CL:0002365
      label: medullary thymic epithelial cell
  biological_processes:
  - preferred_term: T cell differentiation in thymus
    modifier: ABNORMAL
    term:
      id: GO:0033077
      label: T cell differentiation in thymus
  evidence:
  - reference: PMID:18567864
    reference_title: "Common cellular and diverse genetic basis of thymoma-associated myasthenia gravis: role of MHC class II and AIRE genes and genetic polymorphisms."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Recently, we also found that expression of the autoimmune regulator
      (AIRE) gene is absent from approximately 95% of thymomas.
    explanation: >-
      Human thymoma profiling supports AIRE loss as a distinct central-tolerance
      defect in thymoma.
  downstream:
  - target: Central tolerance failure in the thymic microenvironment
    description: Loss of AIRE reduces self-antigen-guided thymocyte deletion.
    evidence:
    - reference: PMID:40983285
      reference_title: "Management of Autoimmune Conditions Associated With Thymic Epithelial Tumors."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        The pathogenesis involves thymic dysfunction leading to impaired T-cell
        development and self-tolerance.
      explanation: >-
        Review-level synthesis supports the edge from intrathymic epithelial
        defects to failure of self-tolerance.
- name: Central tolerance failure in the thymic microenvironment
  biological_scale: TISSUE
  description: >-
    The cortex-dominant, medulla-poor thymoma microenvironment generates
    autoreactive effector T cells and underproduces regulatory T cells, allowing
    self-reactive T-cell escape.
  cell_types:
  - preferred_term: epithelial cell of thymus
    term:
      id: CL:0002293
      label: epithelial cell of thymus
  - preferred_term: medullary thymic epithelial cell
    term:
      id: CL:0002365
      label: medullary thymic epithelial cell
  - preferred_term: regulatory T cell
    term:
      id: CL:0000815
      label: regulatory T cell
  biological_processes:
  - preferred_term: T cell differentiation in thymus
    modifier: ABNORMAL
    term:
      id: GO:0033077
      label: T cell differentiation in thymus
  locations:
  - preferred_term: thymus
    term:
      id: UBERON:0002370
      label: thymus
  evidence:
  - reference: PMID:41098393
    reference_title: "Pathogenesis of thymoma-associated myasthenia gravis: a narrative review."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Since thymomas are mainly composed of the cortex, with few medullae, MG
      may be caused by immature thymoma-derived T cells that fail to undergo
      negative selection and have not yet acquired sufficient self-tolerance.
    explanation: >-
      Transcriptomic and spatial analyses support negative-selection failure as
      a central mechanism linking thymoma to autoimmunity.
  - reference: PMID:18567864
    reference_title: "Common cellular and diverse genetic basis of thymoma-associated myasthenia gravis: role of MHC class II and AIRE genes and genetic polymorphisms."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Generation of autoreactive CD4(+) effector T cells and defective
      production of regulatory CD4(+) T cells inside thymomas contribute to the
      development of myasthenia gravis (MG) in >90% of MG(+) thymomas.
    explanation: >-
      Human thymoma studies support autoreactive effector-T-cell generation and
      deficient Treg production as distinct components of tolerance failure.
  downstream:
  - target: Neuromuscular autoantigen-expressing medullary epithelial niche
    description: Residual medullary-like niches can concentrate MG-relevant antigens.
    evidence:
    - reference: PMID:41098393
      reference_title: "Pathogenesis of thymoma-associated myasthenia gravis: a narrative review."
      supports: SUPPORT
      evidence_source: COMPUTATIONAL
      snippet: >-
        Medullary structures, although much smaller than those of the normal
        thymus, are present in thymomas with MG and MG-susceptible genes are
        clustered.
      explanation: >-
        Residual medullary structures persist specifically in MG-associated
        thymomas, supporting the edge from the tolerance-failing microenvironment
        to a focal autoantigen niche.
  - target: Myasthenia gravis
    description: Autoreactive T-cell escape supports pathogenic neuromuscular autoimmunity.
    evidence:
    - reference: PMID:18567864
      reference_title: "Common cellular and diverse genetic basis of thymoma-associated myasthenia gravis: role of MHC class II and AIRE genes and genetic polymorphisms."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Generation of autoreactive CD4(+) effector T cells and defective
        production of regulatory CD4(+) T cells inside thymomas contribute to the
        development of myasthenia gravis (MG) in >90% of MG(+) thymomas.
      explanation: >-
        Directly asserts the causal contribution of intratumoral tolerance
        failure to myasthenia gravis in the large majority of MG-positive cases.
    - reference: PMID:18401674
      reference_title: "Immunological function of thymoma and pathogenesis of paraneoplastic myasthenia gravis."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        These findings suggest that thymoma generates autoreactive T cells
        causing autoimmunity.
      explanation: >-
        Independent review support for autoreactive T-cell export as the route
        from thymoma to autoimmune disease.
  - target: Pure red cell aplasia
    description: Immune dysregulation can suppress erythroid precursors.
    evidence:
    - reference: PMID:40983285
      reference_title: "Management of Autoimmune Conditions Associated With Thymic Epithelial Tumors."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Myasthenia gravis is the most common, followed by less frequent but
        notable conditions including pure red cell aplasia, Good's syndrome, and
        various neurologic, dermatologic, and systemic autoimmune disorders.
      explanation: >-
        Places pure red cell aplasia within the same thymic-dysfunction-driven
        autoimmune spectrum as myasthenia gravis.
  - target: Good syndrome
    description: Immune dysregulation can coexist with thymoma-associated immunodeficiency.
    evidence:
    - reference: PMID:37729389
      reference_title: "Good's syndrome: brief overview of an enigmatic immune deficiency."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        It was initially considered a thymoma-associated variant of primary
        antibody deficiencies with a reduced or absent number of mature B cells,
        but it later emerged that significant defects of T cell-mediated immune
        functions are the underlying cause of opportunistic infections.
      explanation: >-
        Supports T-cell-compartment dysfunction as the operative defect in Good
        syndrome, consistent with an origin in disturbed intrathymic T-cell
        development. Marked PARTIAL because the same review states that the
        pathophysiology of Good syndrome remains unknown, so the specific edge
        from thymoma tolerance failure to Good syndrome is not established.
  - target: Checkpoint-blockade-unmasked immune-related toxicity
    description: >-
      A pre-existing tolerance defect lowers the threshold for severe autoimmune
      toxicity when PD-1/PD-L1 checkpoints are pharmacologically removed.
    evidence:
    - reference: PMID:36592506
      reference_title: "Immune checkpoint blockers in patients with unresectable or metastatic thymic epithelial tumours: A meta-analysis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The incidence of grade 3-5 ir-AEs was 26.4%, with 17.1% in thymic
        carcinoma and 58.3% in thymoma.
      explanation: >-
        Severe immune-related toxicity is over three times more frequent in
        thymoma than in thymic carcinoma treated with the same agents, which
        tracks the tolerance defect that distinguishes thymoma.
- name: Neuromuscular autoantigen-expressing medullary epithelial niche
  biological_scale: TISSUE
  description: >-
    Myasthenia gravis-associated thymomas contain neuromuscular antigen-expressing
    medullary thymic epithelial populations that organize a local immune niche.
  cell_types:
  - preferred_term: medullary thymic epithelial cell
    term:
      id: CL:0002365
      label: medullary thymic epithelial cell
  evidence:
  - reference: PMID:41098393
    reference_title: "Pathogenesis of thymoma-associated myasthenia gravis: a narrative review."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      By analyzing bulk RNA-sequencing (RNA-seq) and single-cell RNA-seq
      (scRNA-seq) data from thymomas, we identified neuromuscular medullary
      thymic epithelial cells (nmTECs) as neuromuscular antigen-expressing cell
      populations.
    explanation: >-
      Computational analysis of human thymoma transcriptomes supports a
      specialized neuromuscular autoantigen niche relevant to thymoma-associated
      MG.
  - reference: PMID:41098393
    reference_title: "Pathogenesis of thymoma-associated myasthenia gravis: a narrative review."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      We observed spatial nmTEC colocalization and an immune niche, inferring
      an interaction and suggesting a pathological role of nmTECs in MG.
    explanation: >-
      Spatial transcriptomic inference supports a local immune niche downstream
      of thymoma-associated thymic dysarchitecture.
  downstream:
  - target: Myasthenia gravis
    description: Local neuromuscular autoantigen presentation helps focus MG autoimmunity.
    evidence:
    - reference: PMID:41098393
      reference_title: "Pathogenesis of thymoma-associated myasthenia gravis: a narrative review."
      supports: SUPPORT
      evidence_source: COMPUTATIONAL
      snippet: >-
        We observed spatial nmTEC colocalization and an immune niche, inferring
        an interaction and suggesting a pathological role of nmTECs in MG.
      explanation: >-
        Spatial transcriptomic inference supports the neuromuscular autoantigen
        niche acting on myasthenia gravis pathogenesis.
- name: PD-L1 Mediated Adaptive Immune Resistance
  conforms_to: "immune_checkpoint_blockade#Adaptive Immune Resistance"
  biological_scale: CELLULAR
  subtypes:
  - Type B2 thymoma
  - Type B3 thymoma
  description: >-
    Thymoma tumour cells upregulate PD-L1 (CD274), engaging PD-1 on infiltrating
    effector T cells and suppressing anti-tumour cytotoxicity. Expression is not
    uniform across the histologic axis: it is high specifically in the
    lymphocyte-rich cortical types B2 and B3, which is the molecular rationale
    for offering checkpoint blockade in those subtypes. This node is the
    tumour-immune-evasion arm of the entry and is mechanistically separate from
    the central-tolerance arm, even though both converge on checkpoint-inhibitor
    therapy - one as the reason to give it, the other as the reason it is
    dangerous in thymoma.
  cell_types:
  - preferred_term: epithelial cell of thymus
    term:
      id: CL:0002293
      label: epithelial cell of thymus
  biological_processes:
  - preferred_term: negative regulation of T cell mediated immunity
    modifier: INCREASED
    term:
      id: GO:0002710
      label: negative regulation of T cell mediated immunity
  locations:
  - preferred_term: thymus
    term:
      id: UBERON:0002370
      label: thymus
  evidence:
  - reference: PMID:34568003
    reference_title: "Transcriptomic and Mutational Analysis Discovering Distinct Molecular Characteristics Among Chinese Thymic Epithelial Tumor Patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We found high expression of CD274 (PD-L1) in B2 and B3 thymoma samples, and
      validated its expression using immunohistochemistry (IHC).
    explanation: >-
      Transcriptomic detection confirmed at the protein level by IHC establishes
      PD-L1 upregulation in specific thymoma histotypes.
  - reference: PMID:34568003
    reference_title: "Transcriptomic and Mutational Analysis Discovering Distinct Molecular Characteristics Among Chinese Thymic Epithelial Tumor Patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The high expression of PD-L1 in B2 and B3 thymomas support the potential
      application of immunotherapy on certain thymoma subtypes.
    explanation: >-
      The authors draw the therapeutic inference directly, which is what makes
      this node the treatment target rather than merely a descriptive finding.
- name: Checkpoint-blockade-unmasked immune-related toxicity
  biological_scale: ORGANISM
  description: >-
    Pharmacologic PD-1/PD-L1 blockade in thymoma removes a peripheral brake on
    a T-cell repertoire that was already incompletely purged of autoreactive
    clones, producing severe (grade 3-5) immune-related adverse events at a rate
    far above that seen in thymic carcinoma treated with the same agents. This
    node is a treatment-toxicity consequence of the same tolerance defect that
    drives the spontaneous paraneoplastic syndromes, not an independent
    mechanism.
  notes: >-
    Deliberately carries no biological_processes descriptor. The defective
    thymic selection that predisposes to this toxicity is modelled once,
    upstream, on "Central tolerance failure in the thymic microenvironment";
    repeating it here would duplicate a cause onto its own distal consequence.
    The evidence attached to this node is clinical irAE incidence and says
    nothing about any intrathymic process, so no descriptor would be
    evidence-supported here.
  evidence:
  - reference: PMID:36592506
    reference_title: "Immune checkpoint blockers in patients with unresectable or metastatic thymic epithelial tumours: A meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Although immune checkpoint blockers (ICB) are a potential treatment
      strategy, their efficacy seems limited with an increased risk of
      immune-related adverse events (ir-AEs), thus hampering their application in
      daily clinical practice.
    explanation: >-
      Meta-analysis of six phase I/II trials establishes excess immune-related
      toxicity as the dominant limitation of checkpoint blockade in thymic
      epithelial tumours.
  - reference: PMID:36592506
    reference_title: "Immune checkpoint blockers in patients with unresectable or metastatic thymic epithelial tumours: A meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The incidence of grade 3-5 ir-AEs was 26.4%, with 17.1% in thymic
      carcinoma and 58.3% in thymoma.
    explanation: >-
      The thymoma-versus-carcinoma split quantifies the excess toxicity
      attributable to the thymoma-specific tolerance defect.
histopathology:
- name: Thymoma
  finding_term:
    preferred_term: Thymoma
    term:
      id: NCIT:C3411
      label: Thymoma
  frequency: OBLIGATE
  diagnostic: true
  description: >-
    Thymic epithelial neoplasm composed of neoplastic epithelial cells admixed
    with variable numbers of non-neoplastic immature T lymphocytes.
  evidence:
  - reference: PMID:20207296
    reference_title: "[Epithelial tumours of the thymus]."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Epithelial tumours of the thymus include thymomas, thymic carcinomas and
      neuro-endocrine tumours.
    explanation: >-
      Review abstract supports thymoma as a thymic epithelial neoplasm.
phenotypes:
- category: Thoracic
  name: Anterior mediastinal mass
  frequency: OBLIGATE
  diagnostic: true
  description: >-
    Thymoma classically presents as an anterior mediastinal epithelial mass on
    thoracic imaging.
  phenotype_term:
    preferred_term: anterior mediastinal mass
    term:
      id: HP:0033827
      label: Anterior mediastinal mass
  evidence:
  - reference: PMID:37761349
    reference_title: "Thymoma: An Overview."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Thymomas are considered one of the most prevalent types of mediastinal
      epithelial tumors, which frequently develop in the anterior mediastinum.
    explanation: >-
      Review abstract supports the characteristic anterior mediastinal
      presentation of thymoma.
- category: Neuromuscular
  name: Myasthenia gravis
  frequency: FREQUENT
  description: >-
    The dominant autoimmune complication of thymoma, reflecting failure of
    central tolerance and neuromuscular autoantigen presentation.
  phenotype_term:
    preferred_term: myasthenia gravis
    term:
      id: MONDO:0009688
      label: myasthenia gravis
  evidence:
  - reference: PMID:20207296
    reference_title: "[Epithelial tumours of the thymus]."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Thymomas, in particular, can be associated to auto-immune disorders,
      among which predominates myasthenia gravis.
    explanation: >-
      Review abstract identifies myasthenia gravis as the leading autoimmune
      phenotype associated with thymoma.
  - reference: PMID:25521402
    reference_title: "Development of the international thymic malignancy interest group international database: an unprecedented resource for the study of a rare group of tumors."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In total, 38% of patients with thymoma had myasthenia gravis compared with
      less than or equal to 5% for thymic carcinoma and thymic
    explanation: >-
      Quantitative support for the FREQUENT band specifically: 38% in the ITMIG
      international database of 6097 thymic malignancy cases falls in the 30-79%
      HPO frequency range. The contrast with thymic carcinoma also confirms that
      the association is thymoma-specific rather than generic to thymic tumors.
- category: Hematologic
  name: Pure red cell aplasia
  frequency: OCCASIONAL
  description: >-
    Immune-mediated suppression of erythroid precursors causes severe anemia in
    a subset of thymoma patients.
  phenotype_term:
    preferred_term: pure red cell aplasia
    term:
      id: HP:0012410
      label: Pure red cell aplasia
  evidence:
  - reference: PMID:40983285
    reference_title: "Management of Autoimmune Conditions Associated With Thymic Epithelial Tumors."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Myasthenia gravis is the most common, followed by less frequent but
      notable conditions including pure red cell aplasia, Good's syndrome, and
      various neurologic, dermatologic, and systemic autoimmune disorders.
    explanation: >-
      Contemporary review abstract supports pure red cell aplasia as a recurring
      thymoma-associated autoimmune phenotype.
- category: Immunologic
  name: Good syndrome
  frequency: OCCASIONAL
  description: >-
    Thymoma-associated immunodeficiency with hypogammaglobulinemia and increased
    susceptibility to infection.
  phenotype_term:
    preferred_term: Good syndrome
    term:
      id: MONDO:0015696
      label: Good syndrome
  evidence:
  - reference: PMID:39180607
    reference_title: "Good syndrome combined with multiple microbial pulmonary infections: case report and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Good syndrome (GS), a rare acquired immunodeficiency disorder characterized
      by thymoma and hypogammaglobulinemia, predisposes individuals to recurrent
      infections.
    explanation: >-
      Human case-review evidence supports Good syndrome as a bona fide
      thymoma-associated immunodeficiency phenotype.
- category: Immunologic
  name: Recurrent infections
  frequency: OCCASIONAL
  description: >-
    Recurrent bacterial, viral, or opportunistic infections can complicate
    thymoma-associated Good syndrome.
  phenotype_term:
    preferred_term: Recurrent infections
    term:
      id: HP:0002719
      label: Recurrent infections
  evidence:
  - reference: PMID:39180607
    reference_title: "Good syndrome combined with multiple microbial pulmonary infections: case report and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Good syndrome (GS), a rare acquired immunodeficiency disorder characterized
      by thymoma and hypogammaglobulinemia, predisposes individuals to recurrent
      infections.
    explanation: >-
      Human clinical review data supports recurrent infections as a common
      downstream phenotype of thymoma-associated Good syndrome.
- category: Immunologic
  name: Hypogammaglobulinemia
  description: >-
    Reduced circulating immunoglobulin is the defining laboratory abnormality of
    thymoma-associated Good syndrome and the reason immunoglobulin monitoring is
    recommended in thymoma follow-up. No frequency band is asserted: neither
    cited source quantifies how often thymoma patients become
    hypogammaglobulinemic, and per the frequency-evidence SOP an unsupported
    band is worse than none.
  phenotype_term:
    preferred_term: Decreased circulating immunoglobulin concentration
    term:
      id: HP:0004313
      label: Decreased circulating immunoglobulin concentration
  evidence:
  - reference: PMID:37729389
    reference_title: "Good's syndrome: brief overview of an enigmatic immune deficiency."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Good's syndrome, an infrequent adult-onset immunodeficiency is
      characterized by the triad of thymoma, hypogammaglobulinemia, and increased
      susceptibility to recurrent infections.
    explanation: >-
      Hypogammaglobulinemia is one of the three defining components of the
      thymoma-associated Good syndrome triad.
  - reference: PMID:39180607
    reference_title: "Good syndrome combined with multiple microbial pulmonary infections: case report and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Regular immunoglobulin monitoring in thymoma patients is essential for
      early GS diagnosis.
    explanation: >-
      Supports low immunoglobulin as the actionable, monitorable laboratory
      phenotype in thymoma patients.
biochemical:
- name: Anti-titin antibody positivity
  biomarker_term:
    preferred_term: Anti-titin antibody
    term:
      id: NCIT:C101758
      label: Titin
  presence: present
  frequency: FREQUENT
  context: >-
    Measured in myasthenia gravis patients. The FREQUENT band is conditioned on
    the thymectomized MG cohort in which it was established (56 of 70 thymoma
    patients), NOT on unselected thymoma patients, in whom the rate is not
    established by this source.
  specificity: >-
    In thymectomized myasthenia gravis patients, anti-titin antibodies were
    present in 56/70 (80%) of those with thymoma versus 17/165 (10%) of those
    with thymic atrophy or hyperplasia, making them a sensitive marker of thymoma
    in MG patients aged 60 years and younger.
  notes: >-
    Titin is the major autoantigen recognised by anti-striated-muscle antibodies.
    Its diagnostic value is as a prompt to search for an underlying thymoma in a
    myasthenia gravis patient, not as a primary thymoma screening test.
  evidence:
  - reference: PMID:11405802
    reference_title: "Anti-titin antibodies in myasthenia gravis: tight association with thymoma and heterogeneity of nonthymoma patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      anti-titin antibodies were present in most patients with thymoma
    explanation: >-
      Supports the FREQUENT band for anti-titin positivity among thymoma
      patients; the underlying counts are 56/70 thymoma versus 17/165 thymic
      atrophy or hyperplasia.
  - reference: PMID:11405802
    reference_title: "Anti-titin antibodies in myasthenia gravis: tight association with thymoma and heterogeneity of nonthymoma patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Anti-titin antibodies are a sensitive marker of thymoma associated with MG
      in patients 60 years and younger, justifying the insistent search for a
      thymoma in MG patients of this age group who have these antibodies.
    explanation: >-
      States the age-conditioned clinical use of the marker, which is how it
      functions in thymoma workup.
genetic:
- name: GTF2I mutation
  gene_term:
    preferred_term: GTF2I
    term:
      id: hgnc:4659
      label: GTF2I
  association: Recurrent somatic driver mutation
  notes: >-
    GTF2I mutation is highly enriched in type A and AB thymomas and tracks with
    more indolent biology.
  evidence:
  - reference: PMID:24974848
    reference_title: "A specific missense mutation in GTF2I occurs at high frequency in thymic epithelial tumors."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In a series of 274 TETs, we detected the GTF2I mutation in 82% of type A
      and 74% of type AB thymomas but rarely in the aggressive subtypes, where
      recurrent mutations of known cancer genes have been identified.
    explanation: >-
      Human tumor profiling establishes GTF2I as the dominant recurrent somatic
      alteration in indolent thymoma histotypes.
  - reference: PMID:41405018
    reference_title: "Somatic Mutations of Thymic Epithelial Tumors Identified in the Prospective THYMOGENE Trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      GTF2I mutations were prevalent in type A and AB thymomas, in Stage I-II
      tumors, and in patients without myasthenia gravis.
    explanation: >-
      Prospective sequencing confirms the type A/AB enrichment and adds two
      further associations: early stage, and - notably - the ABSENCE of
      myasthenia gravis. The inverse relationship between the GTF2I-mutant
      molecular facet and the autoimmune phenotype is what keeps the oncogenic
      and tolerance-failure axes of this entry separate rather than sequential.
  - reference: PMID:41405018
    reference_title: "Somatic Mutations of Thymic Epithelial Tumors Identified in the Prospective THYMOGENE Trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      GTF2I mutations were the most common, being present in 41% of patients.
    explanation: >-
      Independent prospective cohort estimate of GTF2I mutation frequency across
      unselected thymic epithelial tumours.
- name: HRAS mutation
  gene_term:
    preferred_term: HRAS
    term:
      id: hgnc:5173
      label: HRAS
  association: Recurrent somatic mutation
  notes: >-
    HRAS mutations occur in a minority of thymomas and contribute to the
    low-mutation-burden but recurrently altered molecular landscape.
  evidence:
  - reference: PMID:38338833
    reference_title: "The Molecular Landscape of Thymic Epithelial Tumors: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Thymomas exhibit a limited mutational load, with prevalent GTF2I and HRAS
      mutations.
    explanation: >-
      Review synthesis supports HRAS as one of the recurrent mutations in
      thymoma despite overall low tumor mutational burden.
treatments:
- name: Thymectomy
  description: >-
    Complete surgical resection is the central treatment for localized thymoma
    and can improve coexisting myasthenia gravis.
  treatment_term:
    preferred_term: thymectomy
    term:
      id: NCIT:C29894
      label: Thymectomy
  evidence:
  - reference: PMID:20207296
    reference_title: "[Epithelial tumours of the thymus]."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The initial treatment, as well as that of the recurrence, is based mainly
      on a complete resection.
    explanation: >-
      Review abstract supports complete surgical resection as the core
      treatment of thymoma.
  - reference: PMID:40983285
    reference_title: "Management of Autoimmune Conditions Associated With Thymic Epithelial Tumors."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Surgical intervention through thymectomy remains a cornerstone of
      treatment, particularly for myasthenia gravis, where it can lead to
      considerable symptomatic improvement.
    explanation: >-
      Review abstract supports thymectomy as both oncologic and autoimmune
      disease management in thymoma.
- name: Postoperative radiotherapy
  description: >-
    Adjuvant radiotherapy is used for invasive thymoma, incomplete resection,
    or aggressive histologic subtypes.
  therapeutic_modality: RADIOTHERAPY
  treatment_term:
    preferred_term: radiation therapy
    term:
      id: NCIT:C15313
      label: Radiation Therapy
  evidence:
  - reference: PMID:20207296
    reference_title: "[Epithelial tumours of the thymus]."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Postoperative radiotherapy is systematically added to the treatment of
      invasive tumours and/or to those with an aggressive histological subtype.
    explanation: >-
      Review abstract supports adjuvant radiotherapy for invasive or more
      aggressive thymoma facets.
- name: Platinum-anthracycline chemotherapy
  description: >-
    Cisplatin-based multi-agent chemotherapy is used for unresectable,
    metastatic, or recurrent thymoma.
  treatment_term:
    preferred_term: chemotherapy
    term:
      id: NCIT:C15632
      label: Chemotherapy
    therapeutic_agent:
    - preferred_term: cisplatin
      term:
        id: CHEBI:27899
        label: cisplatin
    - preferred_term: doxorubicin
      term:
        id: CHEBI:28748
        label: doxorubicin
  evidence:
  - reference: PMID:20207296
    reference_title: "[Epithelial tumours of the thymus]."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Inoperable or metastatic tumours require a cisplatine and
      anthracyclin-based chemotherapy, followed by radical surgery and/or
      radiotherapy.
    explanation: >-
      Review abstract supports platinum-anthracycline chemotherapy as the
      standard systemic therapy for unresectable or metastatic thymoma.
- name: Systemic immunosuppression
  description: >-
    Immunosuppressive therapy is often needed when thymoma-associated
    autoimmunity persists or emerges after thymectomy.
  treatment_term:
    preferred_term: immune suppressant agent therapy
    term:
      id: NCIT:C15261
      label: Immunosuppressive Therapy
  evidence:
  - reference: PMID:40983285
    reference_title: "Management of Autoimmune Conditions Associated With Thymic Epithelial Tumors."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      However, autoimmune conditions may persist or even develop after
      thymectomy, necessitating disease-specific approaches with systemic
      immunosuppression.
    explanation: >-
      Review abstract supports systemic immunosuppression for thymoma-associated
      autoimmune complications that are not fully controlled by surgery.
- name: Immune Checkpoint Blockade
  description: >-
    PD-1/PD-L1 blockade (pembrolizumab, nivolumab, avelumab, atezolizumab) has
    activity in pretreated advanced thymic epithelial tumours but is used with
    caution in thymoma specifically. SAFETY CAVEAT: grade 3-5 immune-related
    adverse events occurred in 58.3% of thymoma patients versus 17.1% of thymic
    carcinoma patients in a meta-analysis of six phase I/II trials, so the
    benefit-risk balance is far less favourable in thymoma than in thymic
    carcinoma and close monitoring is required. The excess toxicity is modelled
    in this entry as the "Checkpoint-blockade-unmasked immune-related toxicity"
    pathophysiology node, downstream of the same central-tolerance failure that
    drives the spontaneous paraneoplastic syndromes.
  therapeutic_modality: MONOCLONAL_ANTIBODY
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: pembrolizumab
      term:
        id: NCIT:C106432
        label: Pembrolizumab
  target_mechanisms:
  - target: PD-L1 Mediated Adaptive Immune Resistance
    treatment_effect: INHIBITS
    description: >-
      PD-1/PD-L1 blockade releases the inhibitory signal that thymoma cells
      impose on infiltrating effector T cells, which is the anti-tumour
      rationale for the drug. Note that the toxicity this therapy causes is
      modelled on a separate node reached from the central-tolerance arm, not
      from here.
    evidence:
    - reference: PMID:34568003
      reference_title: "Transcriptomic and Mutational Analysis Discovering Distinct Molecular Characteristics Among Chinese Thymic Epithelial Tumor Patients."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The high expression of PD-L1 in B2 and B3 thymomas support the potential
        application of immunotherapy on certain thymoma subtypes.
      explanation: >-
        Ties the drug to the specific PD-L1 node it acts on, and to the
        histotypes in which that node is active.
  evidence:
  - reference: PMID:36592506
    reference_title: "Immune checkpoint blockers in patients with unresectable or metastatic thymic epithelial tumours: A meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The overall response rate to ICB was 18.4%
    explanation: >-
      Establishes measurable but modest activity. Marked PARTIAL because the
      pooled cohort was 77% thymic carcinoma and only 23% thymoma, so the
      response estimate is not thymoma-specific.
  - reference: PMID:36592506
    reference_title: "Immune checkpoint blockers in patients with unresectable or metastatic thymic epithelial tumours: A meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      our results suggest ICB as a potential strategy in patients with pretreated
      TET, mainly among patients with thymic carcinoma. Close monitoring is
      strongly advised to detect severe immune-toxicity.
    explanation: >-
      The authors' own conclusion steers checkpoint blockade toward thymic
      carcinoma rather than thymoma, which is why this treatment is recorded here
      with an explicit safety caveat rather than as standard therapy.
differential_diagnoses:
- name: Lymphoma
  description: >-
    The main alternative diagnosis for an anterior mediastinal mass in adults,
    and the one whose management diverges most sharply, since lymphoma is treated
    medically rather than by upfront resection.
  disease_term:
    preferred_term: mediastinal malignant lymphoma
    term:
      id: MONDO:0004021
      label: mediastinal malignant lymphoma
  distinguishing_features:
  - Second most common anterior mediastinal tumour in adults after thymic
    epithelial tumours, and far more prominent than thymic tumours in patients
    under 20 years.
  - Lacks the paraneoplastic autoimmune syndromes (myasthenia gravis, pure red
    cell aplasia, Good syndrome) that characterise thymoma.
  - Lacks the organotypic thymic architecture and the admixed immature T
    lymphocytes seen histologically in thymoma.
  - Requires tissue biopsy and medical therapy rather than upfront surgical
    resection, so misclassification changes management directly.
  evidence:
  - reference: PMID:38264756
    reference_title: "Epidemiology of thymomas and thymic carcinomas in the United States and Germany, 1999-2019."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Among patients aged ≥20 years, TETs accounted for the most prevalent
      anterior mediastinal tumors (US/GER: 63%/64%), followed by lymphomas
      (14%/8%).
    explanation: >-
      Quantifies lymphoma as the leading non-thymic alternative for an adult
      anterior mediastinal mass.
- name: Mediastinal germ cell tumor
  description: >-
    The dominant anterior mediastinal tumour of children and young adults, in
    whom thymoma is rare.
  disease_term:
    preferred_term: mediastinal germ cell tumor
    term:
      id: MONDO:0021067
      label: mediastinal germ cell tumor
  distinguishing_features:
  - Predominates in patients under 20 years, an age band in which thymic
    epithelial tumours are distinctly uncommon.
  - Identifiable by serum tumour markers rather than by the autoimmune
    phenomenology that flags thymoma.
  evidence:
  - reference: PMID:38264756
    reference_title: "Epidemiology of thymomas and thymic carcinomas in the United States and Germany, 1999-2019."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      For patients <20 years, predominant tumors included germ cell tumors
      (42%/14%), lymphomas (38%/53%), and TETs (10%/27%).
    explanation: >-
      Establishes the age-dependent inversion that makes germ cell tumour the
      leading differential in young patients.
discussions:
- discussion_id: gtf2i_mouse_no_autoimmunity
  kind: HUMAN_MODEL_MISMATCH
  attaches_to:
  - pathophysiology#Impaired thymic epithelial progenitor differentiation
  status: OPEN
  prompt: >-
    Why does the Gtf2i-mutant mouse reproduce the thymic epithelial architecture
    defect of human thymoma without reproducing the autoimmunity that defines the
    human disease?
  rationale: >-
    The mouse model recapitulates the upstream half of the dismech causal chain -
    aberrant thymic architecture, impaired medullary differentiation, a
    cortex-like epithelial signature - yet TCR repertoire analysis shows
    intrathymic selection remains efficient and no autoimmunity develops. That
    matters mechanistically, because the disease-level claim in this entry is
    that the medulla-poor architecture is what causes tolerance failure. The
    mouse dissociates the two, implying that either an additional human-specific
    factor is required (the CTLA-4 and PTPN22 risk polymorphisms reported in
    thymoma-associated myasthenia gravis are candidates) or that the relevant
    lesion is the frank neoplastic mass rather than the differentiation skew the
    transgenic reproduces. Curators should not treat this mouse as evidence for
    the autoimmunity arm of the graph.
  proposed_experiments:
  - experiment_id: exp_gtf2i_autoimmune_permissive_background
    name: Gtf2i L424H on autoimmune-permissive genetic backgrounds
    description: >-
      Cross the Gtf2i L424H allele onto autoimmune-permissive backgrounds, or
      combine it with the CTLA-4 and PTPN22 risk variants reported in human
      thymoma-associated myasthenia gravis, and re-assess autoantibody
      development and neuromuscular phenotype. A positive result would show the
      architecture defect is necessary but not sufficient for autoimmunity.
  - experiment_id: exp_gtf2i_mouse_human_epithelium_comparison
    name: Direct comparison of transgenic and human thymoma epithelium
    description: >-
      Compare TCR repertoire and tissue-restricted antigen expression in the
      transgenic epithelium against human thymoma tissue, to establish whether
      the mouse reaches the same degree of AIRE loss and MHC class II reduction
      that human thymomas show. If it does not, the mismatch is one of degree
      rather than of species-specific biology.
  evidence:
  - reference: PMID:36175547
    reference_title: "Human thymoma-associated mutation of the GTF2I transcription factor impairs thymic epithelial progenitor differentiation in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      TCR repertoire analysis of the cytopenic T cell compartment indicates
      efficient intrathymic selection; hence, despite marked homeostatic
      proliferation of T cell clones, autoimmunity is not observed.
    explanation: >-
      The model's authors state directly that autoimmunity does not develop,
      establishing the mismatch against the human phenotype.
  - reference: PMID:36175547
    reference_title: "Human thymoma-associated mutation of the GTF2I transcription factor impairs thymic epithelial progenitor differentiation in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Thus, our transgenic mouse model recapitulates some aspects of the
      pathophysiology of a genetically defined type of human thymoma.
    explanation: >-
      The deliberately hedged claim of only partial recapitulation is the
      authors' own scoping of the model's translational validity.
- discussion_id: mhc_class_ii_mg_paradox
  kind: KNOWLEDGE_GAP
  attaches_to:
  - pathophysiology#Reduced MHC class II antigen presentation
  status: OPEN
  prompt: >-
    If reduced MHC class II expression contributes to tolerance failure, why is
    better-preserved MHC class II expression the feature that actually tracks
    with the presence of myasthenia gravis?
  rationale: >-
    This entry curates reduced MHC class II antigen presentation as a
    tolerance-failure mechanism, and that reduction is real and most pronounced
    in WHO types A and AB. But in the same study, among all the abnormalities
    assessed, only better-preserved MHC class II levels were significantly
    associated with the presence of myasthenia gravis - and myasthenia gravis is
    clinically most frequent in types B1 and B2, not A and AB. A coherent reading
    is that two requirements pull in opposite directions: escape of autoreactive
    clones needs defective negative selection, but their activation still needs
    enough class II to present the neuromuscular autoantigen. This entry
    currently models only the first. Until this is resolved, the reduced-MHC
    class-II node should not be read as a monotonic driver of myasthenia gravis
    risk. Prospective sequencing data point the same way from a different
    direction: GTF2I mutation, which marks the same A/AB histotypes that carry
    the lowest class II, is prevalent specifically in patients WITHOUT myasthenia
    gravis. Any resolution has to account for both observations together.
  proposed_experiments:
  - experiment_id: exp_mhcii_mg_stratified_by_histotype
    name: MHC class II expression versus MG status stratified by WHO histotype
    description: >-
      Stratify MHC class II expression against myasthenia gravis status within
      each WHO histotype, so the histotype confound (A and AB have both the
      lowest class II and the least myasthenia gravis) is separated from any
      independent effect of class II level on risk.
  - experiment_id: exp_nmtec_restricted_class_ii
    name: nmTEC-restricted versus bulk tumour MHC class II
    description: >-
      Test whether MHC class II expression restricted to the neuromuscular
      antigen-expressing medullary thymic epithelial cell compartment, rather
      than bulk tumour class II, is what determines myasthenia gravis risk. This
      would reconcile the two directions by locating the requirement for class II
      in a specific niche.
  evidence:
  - reference: PMID:18567864
    reference_title: "Common cellular and diverse genetic basis of thymoma-associated myasthenia gravis: role of MHC class II and AIRE genes and genetic polymorphisms."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Among all theses abnormalities, only better preserved expression levels of
      MHCII (P < 0.001) in thymomas were significantly associated with the
      presence of MG.
    explanation: >-
      States the observation that runs against a simple
      reduced-class-II-drives-MG reading, which is what makes this an open
      question rather than a settled mechanism.
- discussion_id: gtf2i_wildtype_driver_unknown
  kind: KNOWLEDGE_GAP
  attaches_to:
  - pathophysiology#GTF2I-driven thymic epithelial transformation
  status: OPEN
  prompt: >-
    What drives the substantial fraction of thymomas that carry no GTF2I
    mutation and no other detectable somatic driver?
  rationale: >-
    The oncogenic arm of this entry is built almost entirely on GTF2I, which is
    honest to the evidence but covers only part of the disease. Prospective
    sequencing with a thymic-tumour-dedicated 77-gene panel found GTF2I mutations
    in 41 percent of patients and NO mutation at all in 39 percent, and the
    authors report a pattern of mutually exclusive and co-occurring mutations
    suggesting that GTF2I-wildtype thymoma has a distinct pathogenesis rather
    than being a diluted version of the same one. Curators should therefore not
    extend GTF2I-derived mechanism to thymoma as a whole. The gap is partly
    technical - epithelial cells were absent from some dissociated tumours, so
    the driver may be present but unsampled in a lymphocyte-dominated specimen -
    and partly biological, since a non-mutational (epigenetic or structural)
    driver would be invisible to a targeted panel by construction.
  proposed_experiments:
  - experiment_id: exp_gtf2i_wildtype_epithelium_enriched_wgs
    name: Epithelium-enriched whole-genome and methylome profiling of GTF2I-wildtype thymoma
    description: >-
      Apply whole-genome sequencing plus methylation and structural-variant
      calling to flow-sorted or laser-captured epithelial cells from
      GTF2I-wildtype thymomas, so that dilution by the abundant non-neoplastic
      thymocyte compartment cannot mask a driver, and so that non-coding and
      epigenetic drivers invisible to a targeted panel are within reach.
  evidence:
  - reference: PMID:41405018
    reference_title: "Somatic Mutations of Thymic Epithelial Tumors Identified in the Prospective THYMOGENE Trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In 39% of patients, no mutations were found in the 77 genes evaluated.
    explanation: >-
      Quantifies the fraction of thymic epithelial tumours with no identified
      driver even under dedicated targeted sequencing.
  - reference: PMID:41405018
    reference_title: "Somatic Mutations of Thymic Epithelial Tumors Identified in the Prospective THYMOGENE Trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The absence of epithelial cells in some dissociated tumors highlights the
      challenge of identifying mutations in a subset of thymic epithelial tumors
      that lack the GTF2I mutation.
    explanation: >-
      Identifies the sampling artefact that makes part of this gap technical
      rather than biological, which is what the proposed experiment targets.
datasets:
- accession: geo:GSE284479
  title: Altered thymopoiesis in thymoma is associated with defects in negative selection machinery and decreased Treg abundance
  description: Thymomas are rare thymic epithelial tumors harboring a high but variable proportion of lymphocytes without obvious function. Auto-immunity is present in one third of patients at diagnosis. Herein, we performed a phenotypic, scRNAseq, and spatial analysis of both the T cells and tumoral cells. All stages of T cell development -from immature to mature- were present in the tumor suggesting active thymopoiesis in thymoma. However, multiple approaches suggest a maturation blockade at the DN-DP stages. In the mature T cell compartment, the frequency of Tregs was strongly decreased.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: MULTI_OMICS
  sample_count: 53
  publication: PMID:41143696
  notes: Identified by GEO DataSets index search for Thymoma (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.
- accession: geo:GSE177522
  title: RNA-Seq analysis of human MEN1-associated thymic carcinoid and thymoma compared to normal thymus
  description: RNA-Sequencing was performed on rRNA-depleted RNA samples that were isolated from formalin fixed paraffin embedded (FFPE) tissue sections of human normal thymus and human thymic tumors of patients with multiple endocrine neoplasia type 1 (MEN1) syndrome.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: BULK_RNA_SEQ
  sample_count: 19
  publication: PMID:34515662
  notes: Identified by GEO DataSets index search for Thymoma (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.
- accession: geo:GSE218549
  title: DNA-Methylation Analysis as a Tool for Thymoma Classification
  description: Thymomas are malignant thymic epithelial tumors that are difficult to diagnose due to their rarity and complex diagnostic criteria. They represent a morphologically heterogeneous class of tumors mainly defined by “organo-typical” architectural features and cellular composition. The diagnosis of thymoma is burdened with a high inter-observer variability and with the problem that some type-specific morphological alterations are rather a continuum than clear-cut. Methylation pattern-based classification may help to increase diagnostic precision, particularly in borderline cases.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: METHYLATION
  sample_count: 122
  publication: PMID:36497358
  notes: Identified by GEO DataSets index search for Thymoma (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.
📚

References & Deep Research

Deep Research

2

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (1)

Augment: Thymoma with causal-edge evidence, epidemiology, and checkpoint toxicity · 2026-08-08T04:46:58Z · View source

Augmented the existing Thymoma entry. Curated as EDIT not CREATE: the duplicate preflight found Thymoma, Thymic_Carcinoma and Thymic_Neuroendocrine_Carcinoma already present on origin/main. Deep research used the claude_code provider, written to research/Thymoma-deep-research-claude_code.md with 17 web searches and 55 citations, read alongside the pre-existing research/Thymoma-deep-research-manual.md. GeneReviews baseline checked by PubMed esearch: no GeneReviews article exists for thymoma, which is non-Mendelian, so no baseline applied. Added evidence to all 8 previously bare pathophysiology causal edges. Added a new node, Impaired thymic epithelial progenitor differentiation, bridging the GTF2I oncogenic axis to the medulla-poor architecture. Added a new node, Checkpoint-blockade-unmasked immune-related toxicity, capturing the 58.3 versus 17.1 percent grade 3-5 irAE split between thymoma and thymic carcinoma. Added structured prevalence from US and German registry annual incidence, progression covering onset and Masaoka-Koga stage and tumor size, classifications ONCOLOGY_HEMATOLOGY and IMMUNE_RHEUMATOLOGIC, a hypogammaglobulinemia phenotype, an anti-titin antibody biochemical marker, two differential diagnoses, an Immune Checkpoint Blockade treatment carrying an explicit safety caveat, frequency-specific evidence for the myasthenia gravis FREQUENT band at 38 percent in the ITMIG database of 6097 cases, and subtype evidence for types B1 and B2 and encapsulated thymoma. Two discussions recorded: a HUMAN_MODEL_MISMATCH, since the Gtf2i L424H mouse reproduces the epithelial architecture defect but explicitly does not develop autoimmunity, and a KNOWLEDGE_GAP, since better-preserved rather than reduced MHC class II tracks with myasthenia gravis presence, which cuts against a monotonic reading of the reduced-class-II node. Three deep-research errors were caught and not propagated: the report gave MONDO:0006451, which is thymic carcinoma, for thymoma; it gave HGNC:4661, which is GTF2IRD1, for GTF2I; and it labelled HP:0002850 as IgG when the term is IgM. The entry retains the OAK-verified MONDO:0006456 and hgnc:4659. A germ cell tumor MONDO ID that I drafted incorrectly was caught by term validation and replaced with MONDO:0021067. Mass-effect phenotypes of chest pain, cough and dyspnea were deliberately not added because no quotable abstract-level source was found for them. Validation: just validate passed, just count-verified-snippets reports 66 of 66 verified, and just validate-disorders, the batched schema plus terms plus references sweep that CI runs, passed with 66 of 66 and no issues. Compliance rose from 87.4 to 94.1 percent.

Claude Code ▸
Thymoma: Comprehensive Disease Characteristics Research Report
claude-haiku-4-5-20251001, claude-sonnet-5 55 citations 2026-08-08T04:22:23.332525

Thymoma: Comprehensive Disease Characteristics Research Report

1. Disease Information

Overview: Thymoma is a thymic epithelial neoplasm (TET) arising from the epithelial cells of the thymus gland, the primary lymphoid organ situated in the anterior superior mediastinum responsible for T-cell development and central immune tolerance. Thymoma is the most common tumor of the anterior mediastinum in adults and the most common form of thymic epithelial neoplasm, distinguished from thymic carcinoma (historically "type C") by retention of organotypical thymic architecture and lower-grade cytologic atypia (Orphanet: Thymoma; Thymoma: An Overview, PMC10527963).

Key identifiers: - OMIM: 274230 - MONDO: MONDO:0006451 - Orphanet: ORPHA:99867 - ICD-10-CM: C37 (Malignant neoplasm of thymus) - MeSH: D013945 - Related entity — Good syndrome (immunodeficiency with thymoma): a distinct paraneoplastic/associated condition

Synonyms: Thymic epithelial tumor (encompassing thymoma and thymic carcinoma), thymic neoplasm; historically "benign" vs "malignant" thymoma terminology has been abandoned in favor of WHO histologic typing plus staging, since even encapsulated thymomas can recur or metastasize.

Data source note: Information below is derived primarily from aggregated disease-level resources — population cancer registries (SEER, national cancer registries), multi-institutional genomic cohorts (TCGA, AACR GENIE, THYMOGENE trial), and case-series/case-report literature for paraneoplastic phenomenology — rather than individual EHR-level data, consistent with the rarity of the disease.

2. Etiology

Disease Causal Factors: Thymoma's etiology is predominantly somatic/molecular rather than classically genetic or environmentally driven. Unlike most solid tumors, thymomas have a remarkably low overall somatic mutation burden but a striking recurrent driver: a single hotspot missense mutation in GTF2I (general transcription factor IIi).

Risk Factors: - Genetic: No established Mendelian susceptibility locus for sporadic thymoma; GTF2I mutation is somatic, not germline. No strong GWAS-identified common-variant susceptibility loci are established for thymoma (a genuine knowledge gap — rarity limits GWAS power). - Environmental: A European case–control study found an association between prior chest/medical irradiation and thymoma risk that persisted even excluding exposures within 5 years of interview, "suggesting a possible real association or a common pathogenesis involving conditions leading to X-rays" (Constitutional Factors and Irradiation as Risk Factors for Thymoma: A European Case–Control Study, PMC11431288). - Demographic: Age is the dominant risk correlate — incidence rises through middle age and peaks in the 7th decade (70–74 years, ~1.06/100,000) (Frontiers Oncology epidemiology study, PMC10805269). Racial/ethnic variation is notable: Asian/Pacific Islanders have the highest incidence, followed by Black then White populations, and thymoma arises in Black patients at a markedly younger median age (48 vs. 58 years in White patients) (Epidemiology of Thymoma and Associated Malignancies, JTO). - Autoimmune disease is both a risk correlate and consequence: myasthenia gravis (MG), systemic lupus erythematosus, and rheumatoid arthritis co-occur with thymoma at rates far above the general population, likely reflecting shared/bidirectional pathophysiology (below) rather than classic exogenous risk exposure.

Protective Factors: No established genetic or environmental protective factors are documented in the literature for thymoma specifically — this is a notable gap given the rarity of the tumor and paucity of population-scale genetic studies.

Gene-Environment Interactions: No specific validated GxE interaction has been characterized for thymoma; the irradiation-association data above is the closest documented environmental modifier, but no interaction with a specific genetic susceptibility background has been demonstrated.

3. Phenotypes

Thymoma phenotypes fall into three broad classes: (a) local mass-effect/compressive symptoms, (b) systemic paraneoplastic autoimmune syndromes (the clinically dominant and best-characterized phenotype category), and (c) incidental radiographic findings.

A. Local/compressive phenotypes

  • Chest pain, cough, dyspnea from mediastinal mass effect
  • Superior vena cava syndrome (in locally advanced disease)
  • Suggested HPO terms: HP:0100749 (Chest pain), HP:0002094 (Dyspnea), HP:0012735 (Cough)
  • ~30% of patients are asymptomatic, with thymoma discovered incidentally on chest imaging (Update in diagnostic imaging of the thymus, PMC6755948)

B. Paraneoplastic autoimmune phenotypes (the defining clinical feature class)

Phenotype characteristics

  • Onset: Adult-onset overwhelmingly (median age ~59–60 years); rare in children/young adults.
  • Frequency data: MG 30–50% of thymoma cases; Good syndrome up to 5%; asymptomatic/incidental ~30%.
  • Severity/progression: Highly variable — paraneoplastic MG can range from mild ocular symptoms to myasthenic crisis requiring ventilatory support; symptoms may persist, improve, or (rarely) worsen post-thymectomy.
  • Quality of life impact: MG-related fatigue and weakness substantially affect activities of daily living; Good syndrome's recurrent/opportunistic infections and its "ominous prognosis with high mortality rate secondary to recalcitrant infectious disease" represent a severe QoL and survival burden (per Good syndrome literature above). Dedicated thymoma-specific EQ-5D/SF-36 data are sparse in the literature reviewed.

4. Genetic/Molecular Information

Causal/driver gene: - GTF2I (7q11.23; HGNC:4661) — somatic hotspot mutation p.(Leu424His) (also written L404H), a gain-of-function/oncogenic driver, present in the majority of type A/AB thymomas and declining in frequency through B1→B2→B3→thymic carcinoma. This is the single most important molecular lesion described for thymoma (PMC7466068; GTF2I Mutation in Thymomas: Independence From Racial-Ethnic Backgrounds, PMC8419886). - Suggested GO term for GTF2I molecular function: GO:0003713 (transcription coactivator activity).

Variant classification/consequence: - Somatic, not germline; single recurrent missense hotspot (not a spectrum of LOF alleles) — functionally characterized as oncogenic gain-of-function based on mouse knock-in data (Section 6/15). - Note for schema mapping: this would be a functional_impact_category: GAIN_OF_FUNCTION (qualitative, non-ontology-bound) event on GeneticContext, distinct from a quantitative modifier.

Genomic differences by histotype/tumor type (thymic carcinoma diverges sharply): - Thymic carcinomas show a genuinely distinct, higher-mutation-burden genomic profile dominated by TP53 (~27.7% mutated), CYLD (~17.6%), and CDKN2A (~12.1%), with recurrent homozygous 9p21.3 deletions encompassing CDKN2A/CDKN2B (Genomic Landscape of Thymic Carcinoma, AACR GENIE cohort, PMC12839660). - Targeted NGS of thymic epithelial tumors found pathogenic variants in KIT, ERBB2, KRAS, and TP53 in ~30% of thymic carcinomas, informing candidate targeted-therapy strategies (PMC9324890). - MTOR mutations were enriched in local recurrences and lymph node metastases, implicating a progression-associated pathway. - The THYMOGENE prospective trial confirms these findings in an independent prospective cohort (Somatic Mutations of Thymic Epithelial Tumors, THYMOGENE, PMID:41405018).

Prognostic significance of genotype: GTF2I-mutant TETs show a markedly better clinical course than GTF2I-wildtype tumors — 10-year survival 96% vs. 70% (GTF2I gene mutation, Mediastinum) — i.e., the driver mutation correlates inversely with aggressiveness, opposite to the typical oncogene paradigm and consistent with GTF2I-mutant tumors being enriched in the more indolent A/AB histotypes.

Modifier genes: No well-validated modifier genes distinct from co-occurring TP53/CDKN2A alterations in progression to carcinoma have been firmly established; genomic clustering analyses have identified molecular subtypes independent of WHO histologic type, suggesting additional unrecognized modifiers (Genomic clustering analysis, PMC8202771).

Epigenetic information: Advanced/carcinoma-grade tumors show mutations in epigenetic/chromatin-remodeling regulators, though this is less well-characterized than in thymoma proper — an area flagged as needing further multi-omic study.

Chromosomal abnormalities: Recurrent 9p21.3 homozygous deletion (CDKN2A/CDKN2B) in thymic carcinoma; broader cytogenetic literature (6p21/HLA-region associations) was not substantively returned by current searches — worth flagging as not confirmed by primary sources reviewed here (a gap rather than a stated negative).

5. Environmental Information

  • Environmental factors: Prior chest/mediastinal irradiation is the most substantiated environmental risk correlate identified in case–control data (PMC11431288). Suggested ECTO term: exposure to ionizing radiation (therapeutic/diagnostic).
  • Lifestyle factors: No specific validated lifestyle risk factor (smoking, diet, alcohol) is established for thymoma in the literature surveyed — distinguishing it from most epithelial cancers where tobacco/lifestyle exposures dominate.
  • Infectious agents: No infectious etiology is established for thymoma itself. (Contrast: Good syndrome, a thymoma-associated immunodeficiency, predisposes to secondary opportunistic infections — CMV, Pneumocystis jirovecii, mucocutaneous Candida — but these are a consequence of the paraneoplastic immunodeficiency, not a cause of the tumor.)

6. Mechanism / Pathophysiology

Thymoma pathophysiology operates on two largely independent but converging axes: (A) the oncogenic transformation of thymic epithelial cells, and (B) the disruption of central immune tolerance that produces the paraneoplastic autoimmune phenotype. These are mechanistically distinct — a curator building a causal chain should model them as parallel branches from the same initiating cellular context rather than a single linear pathway.

A. Oncogenic transformation pathway

  1. Trigger: Somatic GTF2I p.(L424H) hotspot mutation arising in thymic epithelial progenitor cells (biological_scale: MOLECULAR).
  2. Molecular consequence: GTF2I acts as a transcription factor/coactivator (GO:0003713); the mutant form drives aberrant transcriptional programs in thymic epithelium. Knock-in mouse data show the mutation impairs differentiation of bipotent thymic epithelial progenitors, with medullary differentiation particularly affected (Human thymoma-associated mutation of GTF2I impairs thymic epithelial progenitor differentiation in mice, PMID:36175547; Nature Communications Biology).
  3. Cellular consequence: Aberrant thymic epithelial architecture, reduced thymopoietic activity, and — over time in aged mice — frank tumor formation (biological_scale: CELLULAR/TISSUE) (A Knock-in Mouse Model of Thymoma with the GTF2I L424H Mutation, PMID:36049655 / PMC9691559).
  4. Progression branch (thymic carcinoma): Acquisition of additional drivers — TP53 inactivation, CDKN2A/CDKN2B loss (9p21.3 deletion), CYLD mutation — associated with loss of organotypic architecture, higher-grade cytologic atypia, and worse prognosis (biological_scale: MOLECULAR→TISSUE).

Suggested GO biological process terms: GO:0060218 (hematopoietic stem cell differentiation, analog for epithelial progenitor context), GO:0001756 (somitogenesis-unrelated — better: GO:0060713, labyrinthine layer thymic epithelial differentiation-adjacent terms should be verified via OAK); GO:0009887 (animal organ morphogenesis) as a general placeholder pending precise term verification.

B. Autoimmunity / central-tolerance-failure pathway (drives the paraneoplastic phenotype)

  1. Mechanistic hypothesis (well-supported): Thymomas — particularly cortical-type/epithelial architecture-dominant subtypes — lack a functional medulla, the compartment where professional antigen-presenting medullary thymic epithelial cells (mTECs) normally express AIRE (autoimmune regulator) and drive promiscuous tissue-restricted antigen expression for negative selection of autoreactive thymocytes (Central tolerance to self revealed by the autoimmune regulator, PMC4654700; Update on Aire and thymic negative selection).
  2. Consequence: Failure of this AIRE-dependent negative-selection checkpoint within the neoplastic thymic microenvironment allows export of autoreactive T cells into the periphery — "thymomas may lack the functional medulla where professional antigen-presenting cells engage in negative selection, leading thymomas to generate autoreactive T cells causing autoimmunity" (Immunological function of thymoma and pathogenesis of paraneoplastic MG, PMID:18401674).
  3. Downstream autoantibody generation: Autoreactive T/B cell cooperation produces autoantibodies against neuromuscular junction nicotinic acetylcholine receptor (AChR) components and against striated-muscle antigens (notably titin, a giant sarcomeric protein) — titin main immunogenic region antibodies detected in 97% of thymoma-associated MG sera vs. essentially absent in healthy controls (Immunological and Structural Characterization of Titin Main Immunogenic Region, PMC9952892; Anti-titin antibodies in myasthenia gravis: tight association with thymoma, PMID:11405802).
  4. Clinical manifestation: Neuromuscular junction blockade (myasthenia gravis), or — in Good syndrome — B-cell/T-cell combined immunodeficiency with hypogammaglobulinemia, presumably reflecting a distinct (less well fully elucidated) disruption of B-cell maturation/tolerance rather than simple autoreactivity.

Suggested CL terms: CL:0002365 (medullary thymic epithelial cell), CL:0002365-adjacent cortical thymic epithelial cell term (verify exact CL ID via OAK), CL:0000542 (lymphocyte), CL:0000084 (T cell).

Immune-checkpoint axis (relevant to treatment-toxicity mechanism)

  • Thymomas frequently express high levels of PD-L1, making PD-1/PD-L1 blockade mechanistically rational as an anti-tumor strategy, but the same defective central-tolerance environment that causes paraneoplastic autoimmunity markedly predisposes to severe/fatal immune-related adverse events upon checkpoint inhibition (myocarditis, myositis, hepatitis) — "the thymus is a lymphatic system organ for the development of the immune system, which might contribute to high rates of immune-therapy related toxicity events (irAEs)" (Fatal Toxicity Induced by anti-PD-1 ICI in Thymic Epithelial Tumor; case reports of fatal multi-organ irAEs, Clinical Lung Cancer). This is a directly relevant treatment→target_mechanisms and toxicity-mechanism pattern (could map to the drug_hypersensitivity_scar-adjacent immune-toxicity family, though mechanistically distinct — T-cell-mediated organ toxicity via checkpoint blockade rather than HLA-restricted drug hypersensitivity).

Molecular profiling / advanced technologies

  • Transcriptomics/genomics: TCGA and independent genomic clustering studies have defined molecular subtypes of thymic epithelial tumors that cross-cut WHO histologic classification (PMC8202771).
  • Single-cell/spatial: Not substantively returned in this search pass — likely an emerging-data gap for thymoma specifically, relative to more common cancers.

7. Anatomical Structures Affected

Organ level: - Primary: Thymus (anterior/superior mediastinum) — suggested UBERON:0002370 (thymus). - Secondary/complication sites: pleura (thymoma-associated pleural effusion/pleural dissemination — a characteristic pattern of thymoma spread is direct pleural seeding rather than distant hematogenous metastasis in early stage disease), pericardium, great vessels, lung (direct invasion in advanced Masaoka-Koga stage III–IV), lymph nodes and distant organs in metastatic disease. - Body systems: primarily the immune/lymphatic system (as the originating organ of adaptive immunity) and secondarily neuromuscular system (via paraneoplastic MG) and hematologic/hematopoietic system (via paraneoplastic cytopenias, Good syndrome).

Tissue/cell level: - Neoplastic epithelial cells: cortical- and medullary-type thymic epithelial cells depending on histologic subtype (CL:0002365 medullary TEC and cortical TEC equivalent). - Non-neoplastic but pathologically important "background" population: intratumoral immature T-lymphocytes (thymocytes), which are typically abundant, especially in B-type thymomas, and contribute to the paraneoplastic-autoimmunity mechanism.

Subcellular level: Not a classical organelle-level disease; the driver lesion (GTF2I) acts at the nuclear transcription-factor level (GO cellular component: GO:0005634, nucleus).

Localization: Virtually always anterior mediastinal in location; bilateral/unilateral distinction is not typically applicable (thymus is a midline, though bilobed, organ) — lateralization is not a meaningful phenotype axis here, unlike in paired-organ diseases.

8. Temporal Development

  • Onset: Adult-onset disease; median age at diagnosis ~59–60 years, rare before age 30, exceedingly rare in children (<1% of cases in the 1–18 age band per SEER-linked cohort data) (PMC7138550).
  • Onset pattern: Typically insidious — many patients (~30%) are asymptomatic and diagnosed incidentally on imaging; symptomatic presentation (mass effect or paraneoplastic autoimmune symptoms) develops gradually.
  • Staging (disease "progression" framework): The Masaoka-Koga system (stage I–IVb, based on capsular invasion, extension into surrounding fat/pleura/pericardium, and metastatic spread) remains the most widely applied staging system; the newer TNM/IASLC-ITMIG system (adopted by AJCC/UICC) is increasingly used in parallel (Masaoka-Koga and TNM Staging System, PMC8582470).
  • 5-/10-year overall survival by Masaoka-Koga stage: Stage I 96.4%/88.9%; Stage II 95%/89.5%; Stage III 85.4%/72.8% (stage I and II curves overlap, but stage III is clearly worse).
  • 5-/10-year survival by TNM T-stage: T1 95.5%/88.8%; T2 84.8%/70.7%; T3 88%/76.3%.
  • Progression rate: Generally slow/indolent for type A/AB/B1 thymomas; progressively more aggressive through B2→B3→thymic carcinoma, correlating inversely with GTF2I mutation frequency.
  • Disease course pattern: Can be stable for years post-resection in early stage; capable of late recurrence (pleural recurrence is characteristic) even after apparently complete resection, warranting long-term surveillance.
  • Critical periods: Time-of-surgery is the major modifiable intervention window — complete (R0) resection is the single strongest determinant of outcome; presence of paraneoplastic MG can complicate perioperative anesthetic/respiratory management and requires pre-operative optimization (e.g., plasmapheresis/IVIG or pyridostigmine) in some cases.

9. Inheritance and Population

Epidemiology: - Overall US incidence: variably reported ~0.13–2.2 per million/100,000 person-years depending on cohort and time window studied (Frontiers Oncology, PMC10805269; Trends in incidence of thymoma/thymic carcinoma/thymic NET, PLOS ONE). - Thymomas represented 9,041 cases (66.3% of total thymic cancers) in the US SEER data 2001–2015. - Orphanet cites a European annual incidence estimate of ~1/769,000.

Inheritance pattern: Thymoma is essentially sporadic — driven by a somatic (not germline) GTF2I hotspot mutation. No established Mendelian inheritance pattern, penetrance, expressivity, anticipation, germline mosaicism, or founder-effect data apply to thymoma itself as currently understood. (This contrasts with Good syndrome, which is also an acquired/sporadic adult-onset condition, not inherited.)

Population demographics: - Age distribution (n=4,431 TET patients): 0.6% aged 1–18; 4.0% aged 19–30; 8.6% aged 31–40; 16.7% aged 41–50; 22.0% aged 51–60; 25.0% aged 61–70; 16.6% aged 71–80; 6.5% aged >80 (PMC7138550). - Sex ratio: approximately 1:1.09 (male:female), i.e., roughly equal with a very slight female predominance. - Race/ethnicity: highest incidence in Asian/Pacific Islanders, followed by Black, then White populations; Black patients present at a significantly younger median age (48 vs. 58 years) (JTO epidemiology review). - Geographic distribution: No strong endemic geographic clustering reported beyond the race/ethnicity associations above; comparative US-Germany epidemiologic data (1999–2019) show broadly similar incidence trends across both countries (PMC10805269).

10. Diagnostics

Imaging: - CT (contrast-enhanced) is the imaging modality of choice — evaluates mass size, location, margins (smooth/lobular vs. infiltrative), density, and relationship to adjacent structures (heart, great vessels, lung); helps distinguish thymoma from other anterior mediastinal masses (lymphoma, germ cell tumor, thyroid goiter) (Role of Imaging in Diagnosis, Staging, Treatment of Thymoma, RadioGraphics; Update in diagnostic imaging of thymus, PMC6755948). - MRI is used for further characterization, particularly of cystic vs. solid components.

Biopsy/histopathology: - CT- or ultrasound-guided percutaneous needle biopsy, or surgical resection with histopathology, provides definitive diagnosis via WHO histologic classification. - In classic presentations (imaging + clinical features strongly suggestive), biopsy may be deferred in favor of upfront resection, given seeding risk concerns historically associated with biopsy of encapsulated thymoma (a clinically important nuance for surgical planning).

Serology/biomarkers (central to thymoma-associated MG workup): - Anti-acetylcholine receptor (AChR) antibodies — standard MG diagnostic test. - Anti-titin antibodies — present in 56/70 (80%) of thymectomized thymoma patients vs. only 17/165 (10%) with thymic atrophy/hyperplasia; titin MIR antibodies detected in 97% of thymoma-associated MG sera. Lower sensitivity than CT/MRI for thymoma detection but higher specificity (PMID:11405802; PMC9952892). - Additional autoantibodies reported: anti-ryanodine receptor, anti-striational antibodies.

Genetic/molecular testing: Not yet part of routine standard-of-care diagnostic workup (unlike many other cancers), but GTF2I mutation status (and TP53/CDKN2A in suspected thymic carcinoma) is increasingly assessed in research/clinical-trial contexts (e.g., THYMOGENE) and carries prognostic value.

Clinical criteria/differential diagnosis: Anterior mediastinal mass differential includes thymoma, lymphoma, germ cell tumor, thyroid goiter, thymic cyst, thymic hyperplasia, and thymic carcinoma — WHO histologic typing (A/AB/B1/B2/B3/carcinoma) is the core diagnostic classification framework (2015 WHO Classification of Tumors of the Thymus, PMC4581965; Histologic Classification of Thymoma, JTO; StatPearls Anterior Mediastinal Mass).

Screening: No population-level screening program exists for thymoma given its rarity; incidental detection on chest imaging performed for other indications, or workup triggered by new-onset MG symptoms, are the practical "screening" pathways.

11. Outcome/Prognosis

  • Survival: Strongly stage- and histotype-dependent (see Section 8 for stage-stratified 5-/10-year OS figures). Overall, thymoma carries a substantially better prognosis than thymic carcinoma.
  • Molecular prognostic factor: GTF2I mutation status independently associates with survival — 10-year survival 96% (GTF2I-mutant) vs. 70% (GTF2I-wildtype) (Mediastinum review).
  • Complications:
  • Second primary malignancies (SPM): markedly elevated risk — a SEER analysis found second-cancer incidence of 8,224 per 100,000 thymoma patients vs. 459 per 100,000 in the general SEER population; significantly elevated risk for lung/bronchus cancer, non-basal/squamous skin cancer, urinary bladder cancer, thyroid cancer, and leukemias (ALL, AML, other acute leukemia); no significant increase for lymphoma or hepatobiliary cancers (Epidemiology of Thymoma and Associated Malignancies, JTO; JCO abstract, second primary malignancy). This warrants long-term multi-organ cancer surveillance in thymoma survivors.
  • Paraneoplastic MG and Good syndrome can persist, and in some cases worsen or newly appear, even after thymectomy — thymectomy is not uniformly curative for the autoimmune phenotype.
  • Good syndrome carries a poor prognosis with substantial mortality from recurrent/opportunistic infection.
  • Recurrence pattern: Characteristically pleural/intrathoracic seeding rather than distant hematogenous spread in earlier-stage disease, which shapes surveillance imaging strategy (serial chest CT).
  • Prognostic factors: Masaoka-Koga/TNM stage, WHO histologic subtype, completeness of surgical resection (R0 vs. R1/R2), GTF2I mutation status, and (in thymic carcinoma) TP53/CDKN2A alteration status.

12. Treatment

Surgery (primary modality): - Complete surgical resection (thymectomy, often with removal of surrounding mediastinal fat) is the cornerstone of management for resectable disease. - Minimally invasive (thoracoscopic/robotic) approaches may be considered for clinical stage I–II disease in specialized centers, though NCCN notes these are not yet routinely recommended given limited long-term recurrence/survival data (NCCN guidelines summary). - Suggested NCIT term: NCIT:C15329 (Surgical Procedure) / more specific thymectomy term if available.

Radiotherapy: - Adjuvant radiotherapy (conventionally fractionated, 1.8–2 Gy/day to 45–60 Gy adjuvant, 60–66 Gy definitive) is standard of care for stage II thymoma with capsular invasion after complete resection; elective nodal irradiation is not recommended (NCCN 2.2025 guidelines; Radiotherapy for Thymic Carcinoma, PMC3887269). - Neoadjuvant radiotherapy has been explored for higher-risk B3 thymomas combined with minimally invasive surgery (PMC10076567). - Suggested NCIT term: NCIT:C15313 (Radiation Therapy).

Chemotherapy: - Platinum-based combination chemotherapy is standard of care for unresectable/metastatic or recurrent disease (Cancer Therapy Advisor summary). - Suggested NCIT term: NCIT:C15632 (Chemotherapy).

Targeted therapy: - Sunitinib — recommended for thymic carcinoma regardless of c-KIT mutation status; phase II data showed partial response in 6/23 (26%) chemo-refractory thymic carcinoma patients; STYLE trial showed 21.4% ORR in advanced/recurrent B3 thymoma and thymic carcinoma. - Everolimus (mTOR inhibitor) — durable disease control observed in recurrent thymic epithelial tumors, but with notable risk of fatal pneumonitis — an important toxicity caveat for curation. - These agents map to therapeutic_agent/CHEBI (sunitinib, everolimus) under a treatment_term of Targeted Therapy (NCIT:C93352) or Pharmacotherapy (NCIT:C15986).

Immunotherapy (mechanistically important but high-risk): - Pembrolizumab (anti-PD-1) has shown dramatic remission in some metastatic thymoma cases given high PD-L1 expression, but NCCN does not recommend pembrolizumab for thymoma due to the high rate of immune-related adverse events — fatal multi-organ toxicity (myocarditis, myositis, hepatitis, endocrinopathies) has been reported, mechanistically linked to the same defective central-tolerance thymic microenvironment described in Section 6 (Fatal adverse events in two thymoma patients treated with anti-PD-1; dramatic remission case report, PMC8082155). This is a clinically critical curation point: checkpoint inhibitors are mechanistically rational but carry disproportionate risk in this specific tumor type relative to other PD-L1-high cancers.

Supportive/paraneoplastic-directed care: - Pyridostigmine (acetylcholinesterase inhibitor), immunosuppression, plasmapheresis, or IVIG for paraneoplastic MG management, particularly perioperatively. - Immunoglobulin replacement therapy for Good syndrome-associated hypogammaglobulinemia.

Experimental: Multiple ongoing clinical trials (e.g., NCT04577495 examining prognostic factors post-surgery; various targeted/immunotherapy combination trials) are registered on ClinicalTrials.gov for advanced/refractory thymic epithelial tumors.

Treatment strategy: Multidisciplinary, stage-adapted algorithm — surgery ± adjuvant radiotherapy for early stage; multimodal (chemotherapy ± radiotherapy ± surgery) for locally advanced disease; chemotherapy/targeted therapy for unresectable/metastatic disease, with immunotherapy reserved cautiously given toxicity profile.

13. Prevention

  • Primary prevention: No established primary prevention strategy exists, given the predominantly somatic/sporadic driver-mutation etiology and lack of strong modifiable environmental risk factors beyond incidental/uncommon radiation-exposure associations.
  • Secondary prevention/early detection: No population screening program exists (rarity precludes cost-effective screening); practical early detection occurs via incidental imaging findings or MG-symptom-triggered workup.
  • Tertiary prevention: Long-term surveillance imaging (serial chest CT) post-resection to detect pleural recurrence; long-term multi-organ cancer surveillance given the markedly elevated second-primary-malignancy risk (Section 11); ongoing monitoring/management of paraneoplastic autoimmune phenomena (MG, Good syndrome) independent of oncologic status.
  • Genetic counseling: Not applicable in the traditional sense given the sporadic somatic etiology — no known heritable risk to counsel relatives about.
  • Prophylaxis: Immunoglobulin replacement in diagnosed Good syndrome to reduce opportunistic infection risk; vigilance for opportunistic pathogens (Pneumocystis, CMV) in immunodeficient thymoma patients may warrant prophylactic antimicrobial strategies analogous to other combined immunodeficiencies (extrapolated management principle; not thymoma-specific primary literature identified in this search pass).

14. Other Species / Natural Disease

Naturally occurring veterinary disease — dogs and cats: - Thymoma occurs as a naturally occurring neoplasm in dogs and cats, with a notably parallel paraneoplastic myasthenia gravis phenotype mediated by anti-AChR antibodies, making it a genuine spontaneous comparative model rather than only an induced/engineered one (Acquired myasthenia gravis with concurrent polymyositis and myocarditis secondary to thymoma in a dog, PMC8541714; Metastatic thymoma and acquired generalized MG in a beagle, PMC1716736; Canine Epithelial Thymic Tumors: Outcome in 28 Dogs Treated by Surgery, PMC8698125). - Notable species difference in penetrance of the paraneoplastic phenotype: In cats presenting with MG, roughly 1 in 4 has a thymic/mediastinal mass, whereas in dogs only ~3–4% of MG cases are thymoma-associated — cats show a much tighter thymoma–MG linkage than dogs (Merck Veterinary Manual, Neurological Paraneoplastic Syndromes in Small Animals; Myasthenia Gravis in Dogs and Cats, VIN). - Veterinary treatment parallels human management: surgical thymectomy is the mainstay, with pyridostigmine/anticholinesterase therapy for MG symptom control. - No OMIA (Online Mendelian Inheritance in Animals) entry or dog/cat GTF2I ortholog mutation data were identified in this search pass — veterinary thymoma appears to be studied predominantly at the clinical/phenotypic level rather than the somatic-genomic level, representing a translational research gap.

Comparative biology: The conserved thymoma→paraneoplastic-MG mechanism (loss of medullary negative-selection capacity → autoreactive T cells → anti-AChR antibody generation) across humans, dogs, and cats supports this as an evolutionarily conserved thymic-tolerance failure mechanism rather than a human-idiosyncratic phenomenon, strengthening confidence in the Section 6 mechanistic model.

Zoonotic potential: Not applicable — thymoma is a non-transmissible neoplastic disease.

15. Model Organisms

Genetically engineered mouse model (the primary validated model): - A conditional Gtf2i(L424H) knock-in mouse (mutation targeted to Foxn1+ thymic epithelial cells) is the first genuine animal model of thymoma and directly demonstrates causality of the human hotspot mutation (A Knock-in Mouse Model of Thymoma with the GTF2I L424H Mutation, PMID:36049655/PMC9691559; editorial: Now We Have the First Animal Model for Thymoma, JTO). - Phenotype recapitulation: In young mice, the mutation impairs thymic medulla development and mTEC maturation (mirroring the human medullary-deficiency mechanism proposed for paraneoplastic autoimmunity); in aged mice, it induces frank thymic tumor formation that histologically mirrors human type B1 and B2 thymomas (PMC7466068; Communications Biology, PMID:36175547). - Model limitations: The mouse model most closely recapitulates B1/B2-type histology rather than the A/AB types where GTF2I mutation frequency is highest in humans (76–83%) — a partial phenotype-genotype mismatch worth flagging as a HUMAN_MODEL_MISMATCH-style consideration if curated into dismech, since the mutation's histologic association differs between the engineered model and the natural human tumor spectrum. This is exactly the kind of translational-validity caveat the project's schema is designed to capture explicitly rather than assume. - Applications: This model enables study of the temporal sequence from mTEC differentiation defect → reduced thymopoiesis → tumorigenesis, and provides a platform for preclinical testing of GTF2I-pathway-directed therapeutics (none yet clinically available, representing a translational opportunity).

Cell-line/in vitro models: Not prominently returned in this search pass; thymic epithelial tumor cell lines are notoriously difficult to establish (a recognized limitation in the field, consistent with the low proliferative/mutational-burden biology of GTF2I-driven tumors), which is part of why the knock-in mouse model represented a significant advance.

Resources: No dedicated thymoma-specific model organism database was identified; models are documented in the primary literature (JTO, Communications Biology) rather than centralized repositories like MGI with a disease-specific portal.

Summary of Key Ontology Term Suggestions for KB Curation

Category Suggested term
Disease MONDO:0006451 (thymoma); OMIM:274230
Related disease Good syndrome / immunodeficiency with thymoma
Gene HGNC:4661 (GTF2I); HGNC:11998 (TP53); HGNC:1787 (CDKN2A)
Cell types CL:0002365 (medullary thymic epithelial cell) and cortical TEC counterpart (verify via OAK); CL:0000084 (T cell)
Phenotypes HP:0003473 (Myasthenia); HP:0004313 (Decreased circulating antibody level); HP:0000508 (Ptosis); HP:0002015 (Dysphagia)
Anatomy UBERON:0002370 (thymus)
Treatment NCIT:C15329 (Surgical Procedure); NCIT:C15313 (Radiation Therapy); NCIT:C15632 (Chemotherapy); NCIT:C93352 (Targeted Therapy)
Therapeutic agents CHEBI (sunitinib, everolimus); NCIT:C20401-class biologics (pembrolizumab)

(All ontology IDs above should be run through OAK verification per dismech SOP before use in a curated entry — none have been independently re-verified against runoak info in this research pass and are offered as starting candidates only.)

Sources

Manual Pubmed Review ▸
Thymoma: curation-oriented mechanistic summary
n/a 9 citations 2026-04-13T05:40:00Z

Thymoma: curation-oriented mechanistic summary

Modeling decisions applied from issue #1198

  • The dismech curation unit is the disease-level mechanism graph, not every oncology ontology subclass. Thymoma therefore remains one disease entry rather than separate pages for WHO types A, AB, B1, B2, B3, or invasion-status variants.
  • disease_term stays MONDO-first as MONDO:0006456 (thymoma).
  • The entry should also carry a disease-level NCIT mapping to NCIT:C3411 (Thymoma), because NCIT is the more oncology-native coding system for downstream cancer interoperability.
  • Subtypes are best represented as flat facet axes. For thymoma, the highest-yield axes are:
  • histological_pattern: Type A (NCIT:C6454), Type AB (NCIT:C6885), Type B1 (NCIT:C6887), Type B2 (NCIT:C6888), Type B3 (NCIT:C7997)
  • invasion_status: Encapsulated thymoma (NCIT:C7386), invasive thymoma (NCIT:C7904)
  • The NCIT-grounded subtype terms are ontology grounding only. They should not imply separate dismech pages or a “Not Yet Curated” renderer state.

Disease overview

Thymoma is a thymic epithelial tumor of the anterior mediastinum whose biology is unusual among solid tumors because the neoplasm also distorts thymic T-cell selection. The two dominant disease-level themes are therefore:

  1. Tumor-cell intrinsic oncogenesis, especially the GTF2I-enriched, low-mutation-burden program of indolent type A/AB thymoma.
  2. Tumor-microenvironment immune dysfunction, in which abnormal thymic epithelial architecture impairs central tolerance and promotes paraneoplastic autoimmunity.

Subtype biology

  • Type A / Type AB thymoma: indolent histotypes with the strongest GTF2I enrichment. PMID:24974848 reports that GTF2I mutation is detected in 82% of type A and 74% of type AB thymomas.
  • Type B1 / Type B2 thymoma: more cortical, lymphocyte-rich histotypes with increasing invasiveness and myasthenia gravis association.
  • Type B3 thymoma: epithelial-predominant thymoma with substantially greater local invasion and worse disease-free survival. PMID:15063231 reports a monotonic increase in neighboring-organ invasion across A → AB → B1 → B2 → B3.
  • Encapsulated vs invasive thymoma: a separate invasion-status axis is useful because clinical behavior spans indolent, organ-confined disease to locally invasive or metastatic disease even within the same broad disease entry (PMID:20207296).

Core mechanisms

1. GTF2I-driven thymic epithelial transformation

  • PMID:24974848: “We analyzed 28 thymic epithelial tumors (TETs) using next-generation sequencing and identified a missense mutation ... in GTF2I at high frequency in type A thymomas, a relatively indolent subtype.”
  • PMID:32034314: “Our findings identify GTF2I mutation as a new oncogenic driver that is responsible for transformation of thymic epithelial cells.”

Interpretation for YAML: this supports a disease node centered on thymic epithelial transformation, with subtype restriction to type A/AB thymoma and downstream linkage to proliferative and metabolic programs.

2. Metabolic stress adaptation downstream of mutant GTF2I

  • PMID:32034314: “Gtf2i L424H knockin cells exhibited cell transformation, aneuploidy, and increase tumor growth and survival under glucose deprivation or DNA damage.”
  • PMID:32034314: “Gtf2i mutation also increased the expression of several glycolytic enzymes, cyclooxygenase-2, and caused modifications of lipid metabolism.”

Interpretation for YAML: metabolic rewiring is worth its own atomic node rather than being bundled into the transformation node.

3. Reduced MHC class II antigen presentation

  • PMID:18567864: “expression levels of class II major histocompatibility complex (MHCII) genes are variably decreased in thymomas, most prominently in histological WHO types A and AB”

Interpretation for YAML: this directly supports an atomic node for reduced antigen presentation via MHC class II, especially in type A/AB thymoma.

4. AIRE loss in thymic epithelial cells

  • PMID:18567864: “expression of the autoimmune regulator (AIRE) gene is absent from approximately 95% of thymomas.”

Interpretation for YAML: AIRE loss should remain separate from reduced MHC II expression because both are central-tolerance defects but represent distinct molecular lesions.

5. Central tolerance failure with autoreactive T-cell escape

  • PMID:41098393: “Since thymomas are mainly composed of the cortex, with few medullae, MG may be caused by immature thymoma-derived T cells that fail to undergo negative selection and have not yet acquired sufficient self-tolerance.”
  • PMID:18567864: “Generation of autoreactive CD4(+) effector T cells and defective production of regulatory CD4(+) T cells inside thymomas contribute to the development of myasthenia gravis (MG) in >90% of MG(+) thymomas.”

Interpretation for YAML: negative-selection failure, autoreactive effector-T-cell generation, and defective Treg production belong in a linked but still atomic disease mechanism chain.

6. Neuromuscular autoantigen niche in MG-associated thymoma

  • PMID:41098393: “we identified neuromuscular medullary thymic epithelial cells (nmTECs) as neuromuscular antigen-expressing cell populations.”
  • PMID:41098393: “We observed spatial nmTEC colocalization and an immune niche, inferring an interaction and suggesting a pathological role of nmTECs in MG.”

Interpretation for YAML: this is a more specific downstream mechanism that helps explain why myasthenia gravis is the dominant autoimmune phenotype.

Hallmark phenotype profile

  • Anterior mediastinal mass: characteristic anatomic presentation (PMID:37761349).
  • Myasthenia gravis: dominant autoimmune phenotype (PMID:20207296).
  • Pure red cell aplasia: recurrent hematologic autoimmune complication (PMID:40983285).
  • Good syndrome and recurrent infections: thymoma-associated immunodeficiency phenotype with hypogammaglobulinemia and infection susceptibility (PMID:39180607).

Treatment implications

  • Complete resection / thymectomy remains the central intervention for localized disease (PMID:20207296; PMID:40983285).
  • Postoperative radiotherapy is mainly relevant for invasive disease or aggressive histology (PMID:20207296).
  • Platinum-anthracycline chemotherapy is the standard systemic approach for inoperable or metastatic thymoma (PMID:20207296).
  • Systemic immunosuppression remains necessary when autoimmune complications persist or newly arise after thymectomy (PMID:40983285).

Ontology grounding used in the YAML

  • Disease anchor: MONDO:0006456 thymoma
  • Disease-level NCIT mapping: NCIT:C3411 Thymoma
  • Histologic subtype grounding:
  • NCIT:C6454 Thymoma Type A
  • NCIT:C6885 Thymoma Type AB
  • NCIT:C6887 Thymoma Type B1
  • NCIT:C6888 Thymoma Type B2
  • NCIT:C7997 Thymoma Type B3
  • Invasion-status subtype grounding:
  • NCIT:C7386 Encapsulated Thymoma
  • NCIT:C7904 Invasive Malignant Thymoma

NCIT subtype identifiers were checked against the EVS neoplasm hierarchy page for thymoma subclasses while keeping the disease anchor MONDO-first in the dismech entry.

References

  • PMID:24974848
  • PMID:32034314
  • PMID:18567864
  • PMID:41098393
  • PMID:15063231
  • PMID:20207296
  • PMID:37761349
  • PMID:39180607
  • PMID:40983285