HER2-Positive Breast Cancer

MONDO:0006244 Pathograph 5 Show in embeddings browser breast carcinoma

HER2-positive breast cancer is a molecularly-defined subtype of breast cancer characterized by amplification or overexpression of the ERBB2 (HER2/neu) gene, encoding a receptor tyrosine kinase. HER2 amplification occurs in approximately 15-20% of breast cancers and historically conferred poor prognosis before the advent of HER2-targeted therapies. The development of trastuzumab revolutionized treatment and established HER2+ breast cancer as a paradigm for targeted therapy in solid tumors. Modern treatment includes multiple HER2-targeted agents including monoclonal antibodies, tyrosine kinase inhibitors, and antibody-drug conjugates.

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5
Pathophys.
1
Histopath.
3
Phenotypes
3
Hypotheses
1
Gaps
5
Pathograph
2
Genes
5
Medical Actions
3
Deep Research
3
Hyp. Reports
🏷

Classifications

Harrison's Chapter
ONCOLOGY_HEMATOLOGY
ICD-O Morphology
Adenocarcinoma
◈

Mechanistic Hypotheses

3
Canonical HER2-GRB2 RTK Effector Model
canonical_grb2_rtk_effector_model CANONICAL
Constitutively activated HER2 receptors create phosphotyrosine docking sites that recruit GRB2 adaptor complexes, coupling receptor activation to canonical RAS-MAPK and PI3K-AKT proliferative signaling. This is the textbook HER2+ breast cancer signaling cascade and the explicit disease-level instantiation of the rtk_grb2_signaling_adaptation module's canonical effector hypothesis.
Deep research
Asta citations 18 citations 2026-05-26T23:12:26.883498
Show evidence (2 references)
PMID:11175341 SUPPORT In Vitro
"the activation of ErbB2 by heregulin or by its overexpression requires Grb2 to stimulate the Akt pathway to propagate mitogenic signals"
Lim et al. directly demonstrate that GRB2 is required for ErbB2-driven Akt activation in heregulin-stimulated and ErbB2-overexpressing breast cancer cells — the canonical adaptor function in HER2+ disease.
PMID:40289214 SUPPORT In Vitro
"GRB2 enhances proliferation, migration, and invasion while suppressing apoptosis in HER2-positive breast cancer cells in vitro, primarily by regulating phosphorylation and alternative splicing of key proteins within the Ras/MAPK pathway."
Wang et al. confirm GRB2's canonical proliferative/MAPK-coupling role in HER2+ breast cancer with phenotypic readouts directly attributable to GRB2 perturbation.
CMTM6 HER2 Stabilization Resistance Model
cmtm6_her2_stabilization_resistance_model EMERGING
Trastuzumab resistance is sustained in part by post-translational stabilization of the HER2 receptor protein at the cell surface. CMTM6 (CKLF-like MARVEL transmembrane domain-containing 6) directly interacts with HER2 and inhibits HER2 ubiquitination, preserving the GRB2-adaptor output even under trastuzumab pressure. Under the interactome- rebalancing framing, CMTM6 acts as a separate post-translational pivot point in parallel to GRB2 conformational state, and degrading or inhibiting CMTM6 may resensitize tumors to HER2-targeted therapy. This hypothesis is independent of (and complementary to) GRB2-level conformational control.
Deep research
Asta citations 18 citations 2026-05-26T23:19:07.703533
Show evidence (2 references)
PMID:36627608 SUPPORT In Vitro
"these findings highlight that CMTM6 stabilizes HER2 protein, contributing to trastuzumab resistance and implicate CMTM6 as a potential prognostic marker and therapeutic target for overcoming trastuzumab resistance in HER2+ breast cancer"
Xu et al. directly establish CMTM6-mediated post-translational HER2 stabilization as a trastuzumab-resistance mechanism.
PMID:36627608 SUPPORT In Vitro
"CMTM6 expression was upregulated in trastuzumab-resistant HER2+ breast cancer cell"
Co-localization, co-immunoprecipitation, and ubiquitination data link CMTM6 expression to the trastuzumab-resistant state.
GRB2 Conformational Pivot Resistance Model
grb2_conformational_pivot_resistance_model EMERGING
GRB2 is a thermodynamic pivot point whose conformational state determines whether HER2-driven tumors funnel into cytoplasmic effector dominance, nuclear RAD51-dependent replication-fork protection, or PARPi-STING innate-immune activation. Allosteric stabilization or PROTAC degradation of GRB2 would select between these interactome states and modulate trastuzumab/TKI resistance. This hypothesis is distinguishable from the canonical effector model by predicting that GRB2 perturbation produces different phenotypes depending on which conformational state is locked, not simply graded loss of adaptor function.
Deep research
Asta citations 18 citations 2026-05-26T23:12:53.534041
Show evidence (2 references)
PMID:38459011 SUPPORT In Vitro
"Growth factor receptor-bound protein 2 (GRB2) is a cytoplasmic adapter for tyrosine kinase signaling and a nuclear adapter for homology-directed-DNA repair."
Dual cytoplasmic/nuclear GRB2 framing motivates the conformational-pivot hypothesis as distinct from the canonical effector model.
PMID:38459011 SUPPORT In Vitro
"In GRB2-depleted cells, PARP inhibitor (PARPi) treatment releases DNA fragments from stalled forks into the cytoplasm that activate the cGAS-STING pathway to trigger pro-inflammatory cytokine production."
Experimental demonstration that loss of GRB2 fork-protection function produces a distinct PARPi-STING vulnerability supports the pivot framing.
?

Discussions and Knowledge Gaps

1
Is the GRB2 adaptor hub a tractable allosteric pivot point for rebalancing the HER2+ breast cancer interactome under HER2-targeted therapy resistance, and does conformational control of GRB2 (versus its degradation) change which adaptive bypass routes the tumor recruits?
KNOWLEDGE GAP OPEN gap_her2_grb2_adaptor_pivot
Attached to
pathophysiology#GRB2 Adaptor Hub pathophysiology#Downstream Oncogenic Signaling
HER2-targeted antibodies and TKIs do not eliminate downstream GRB2 adaptor output: resistant tumors typically rewire RAS-MAPK and PI3K-AKT signaling rather than lose HER2. GRB2 also has a documented nuclear RAD51 fork- protection role under replication stress. Treating GRB2 as a thermodynamic pivot — stabilizing distinct SH2/SH3 conformational states with allosteric binders, or degrading the protein with PROTAC warheads — would let us test whether different perturbations funnel the interactome into distinct pathological survival states (cytoplasmic effector dominance vs. nuclear fork-protection dominance vs. innate-immune activation through PARPi- induced cytosolic DNA).
Proposed experiments
Allosteric GRB2 stabilization versus PROTAC degradation in HER2+ organoids
controlled perturbation experiment
exp_her2_grb2_conformational_pivot
Treat HER2-amplified patient-derived breast cancer organoids and isogenic cell-line panels (HER2-amplified, HER2-amplified plus PIK3CA-mutant, trastuzumab-resistant derivatives) with (a) allosteric GRB2 SH2/SH3 binders tuned to stabilize discrete conformational states, (b) a GRB2- directed PROTAC warhead that physically degrades the adaptor, and (c) paired HER2 inhibition (trastuzumab, tucatinib, T-DXd). Read out RAS- MAPK and PI3K-AKT effector signaling, nuclear GRB2 localization, RAD51 fork-protection at stalled replication forks, cytosolic DNA release, cGAS-STING activation, and immune-cell killing in autologous co-culture. Compare to PARP-inhibitor co-treatment arms to test whether GRB2 pivot state predicts PARPi-STING vulnerability.
Model systems
HER2-amplified patient-derived breast cancer organoid panel
Matched patient-derived organoids spanning trastuzumab-naive, trastuzumab-resistant, and PIK3CA-co-mutant HER2+ disease, paired with autologous immune cells for co-culture readouts.
ORGANOID
human NCBITaxon:9606
mammary gland UBERON:0001911
luminal epithelial cell of mammary gland CL:0002326
Perturbations
Allosteric GRB2 conformational stabilization
pathophysiology#GRB2 Adaptor Hub
Small-molecule allosteric binders tuned to stabilize distinct SH2/SH3 conformational states of GRB2 to test conformation-specific output.
GRB2 hgnc:4566
GRB2 PROTAC degradation
pathophysiology#GRB2 Adaptor Hub
Targeted GRB2 degradation via PROTAC warhead to compare adaptor loss with adaptor conformational locking.
GRB2 hgnc:4566
Effect: DECREASED
PARP inhibitor replication-stress challenge
pathophysiology#GRB2 Adaptor Hub
Co-administer PARP inhibitor to test whether GRB2 conformational state gates PARPi-induced cytosolic DNA and cGAS-STING activation.
Readouts
RAS-MAPK and PI3K-AKT effector output
pathophysiology#Downstream Oncogenic Signaling
MAPK cascade GO:0000165
Direction: POSITIVE
Nuclear GRB2 / RAD51 fork-protection and innate-immune activation
pathophysiology#GRB2 Adaptor Hub
DNA damage response GO:0006974 innate immune response GO:0045087
Direction: NEGATIVE
Interpretation: Loss of nuclear GRB2 / RAD51 fork-protection together with increased innate-immune activation under PARP inhibition would support a conformation-gated state switch.
Decision criterion
The conformational pivot model is supported if allosteric stabilization and PROTAC degradation produce distinct effector versus DDR phenotypes in matched HER2+ models, and if at least one perturbation sensitizes trastuzumab-resistant lines to PARP-inhibitor-driven cytosolic DNA and cGAS-STING activation.
Would support
pathophysiology#GRB2 Adaptor Hub pathophysiology#Downstream Oncogenic Signaling
Show evidence (1 reference)
PMID:38459011 SUPPORT In Vitro
"In GRB2-depleted cells, PARP inhibitor (PARPi) treatment releases DNA fragments from stalled forks into the cytoplasm that activate the cGAS-STING pathway to trigger pro-inflammatory cytokine production."
Provides the experimental precedent for GRB2 perturbation plus PARP inhibition producing cytosolic DNA and innate immune activation, which the HER2+ experiment generalizes to a conformational-pivot framing.
⚙

Pathophysiology

5
ERBB2 Gene Amplification
HER2-positive breast cancer is driven by amplification of the ERBB2 gene on chromosome 17q12, resulting in overexpression of the HER2 receptor tyrosine kinase. Gene amplification typically results in 25-50 copies per cell, leading to massive receptor overexpression on the cell surface.
luminal epithelial cell of mammary gland CL:0002326
ERBB2 signaling pathway GO:0038128 ↑ INCREASED
Downstream
Constitutive Receptor Activation Receptor overexpression leads to ligand-independent dimerization and activation
Show evidence (2 references)
PMID:40303293 PARTIAL
"HER2-positive breast cancer, which accounts for approximately 15-20% of all breast cancers, is characterized by its aggressive recurrence, metastasis and reduced survival."
This abstract identifies HER2-positive breast cancer as a distinct, aggressive subtype, supporting the disease definition used here.
CIVIC_ASSERTION:2 SUPPORT Other
"HER2 amplification defines a clinically relevant subtype of breast cancer."
CIViC's accepted assertion supports ERBB2/HER2 amplification as the defining molecular feature of HER2-positive breast cancer.
Constitutive Receptor Activation
Massive HER2 overexpression promotes spontaneous receptor homodimerization and heterodimerization with other ERBB family members (EGFR, HER3, HER4) without ligand binding. The phosphorylated receptor tail creates docking sites for SH2- domain-containing adaptors including GRB2, instantiating the RTK-phosphotyrosine docking trigger of the GRB2 signaling adaptation module.
transmembrane receptor protein tyrosine kinase signaling pathway GO:0007169 ↑ INCREASED protein autophosphorylation GO:0046777 ↑ INCREASED
Downstream
GRB2 Adaptor Hub Phosphorylated HER2 recruits GRB2-containing adaptor complexes at pY docking sites.
GRB2 Adaptor Hub
GRB2 is the adaptor control point that couples HER2 phosphotyrosine docking to downstream effector complexes. In HER2-amplified breast tumors, the GRB2 adaptor function is constitutively engaged through ERBB2 homo- and heterodimers, driving sustained RAS-MAPK and PI3K-AKT signaling. The HER2 amplicon at 17q12 frequently co-amplifies GRB7, an SH2 adaptor whose expression correlates with GRB2-pathway output and adverse outcome. A second, nuclear GRB2 function in RAD51-dependent replication-fork protection may rebalance the tumor's interactome toward DNA-damage tolerance under HER2-targeted or chemotherapy-induced replication stress.
GRB2 hgnc:4566 GRB7 hgnc:4567
growth factor receptor binding GO:0070851
Downstream
Downstream Oncogenic Signaling Cytoplasmic GRB2 adaptor complexes activate RAS-MAPK and PI3K-AKT.
Show evidence (3 references)
PMID:11175341 SUPPORT In Vitro
"the growth factor receptor bound protein-2 (Grb2) is required for the proliferation of ErbB2-overexpressing breast cancer cells"
Lim et al. directly establish GRB2 as a required adaptor for ErbB2- driven proliferation in HER2+ breast cancer cells, instantiating the module's GRB2 Adaptor Hub node in this disease.
PMID:38459011 SUPPORT In Vitro
"Growth factor receptor-bound protein 2 (GRB2) is a cytoplasmic adapter for tyrosine kinase signaling and a nuclear adapter for homology-directed-DNA repair."
Establishes the dual cytoplasmic/nuclear GRB2 framing relevant to HER2+ tumors under replication stress.
PMID:23628726 PARTIAL
"HER2 gene amplification is observed in about 15% of breast cancers."
The HER2 amplicon frequently extends to include GRB7, providing a structural basis for amplified GRB2-pathway adaptor output in this subtype.
Downstream Oncogenic Signaling
Activated HER2 signals through PI3K-AKT-mTOR and RAS-RAF-MEK-ERK pathways, promoting cell proliferation, survival, and resistance to apoptosis. HER2-HER3 heterodimers are particularly potent activators of the PI3K pathway. Adaptive rewiring of these outputs (rather than HER2 loss) is the dominant resistance pattern under trastuzumab and tyrosine kinase inhibition.
phosphatidylinositol 3-kinase signaling GO:0043491 ↑ INCREASED MAPK cascade GO:0000165 ↑ INCREASED
Downstream
Uncontrolled Proliferation Sustained signaling drives tumor growth
Show evidence (1 reference)
PMID:40289214 SUPPORT In Vitro
"GRB2 enhances proliferation, migration, and invasion while suppressing apoptosis in HER2-positive breast cancer cells in vitro, primarily by regulating phosphorylation and alternative splicing of key proteins within the Ras/MAPK pathway."
Documents the Ras/MAPK proliferative and pro-survival output downstream of GRB2 in HER2-positive breast cancer cells.
Uncontrolled Proliferation
Constitutive HER2 signaling drives continuous cell cycle progression and resistance to apoptotic signals. HER2+ tumors are typically high grade with high proliferation indices (high Ki-67).
cell population proliferation GO:0008283 ↑ INCREASED
Show evidence (1 reference)
PMID:40289214 SUPPORT In Vitro
"GRB2 enhances proliferation, migration, and invasion while suppressing apoptosis in HER2-positive breast cancer cells in vitro, primarily by regulating phosphorylation and alternative splicing of key proteins within the Ras/MAPK pathway."
Documents enhanced proliferation and suppressed apoptosis in HER2-positive breast cancer cells driven by sustained Ras/MAPK signaling.
✶

Histopathology

1
Invasive Ductal Carcinoma VERY_FREQUENT
Invasive ductal carcinoma is the most common type of breast cancer.
Show evidence (1 reference)
PMID:39806949 PARTIAL
"Invasive ductal carcinoma (IDC) is the most common type of breast cancer,"
Abstract states that invasive ductal carcinoma is the most common breast cancer type.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for HER2-Positive Breast Cancer Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

3
Breast 1
Breast Carcinoma OBLIGATE Breast carcinoma HP:0003002
Show evidence (1 reference)
PMID:39806949 SUPPORT Human Clinical
"Invasive ductal carcinoma (IDC) is the most common type of breast cancer,"
HER2-positive tumors are typically invasive ductal (breast) carcinomas, supporting breast carcinoma as the defining neoplastic phenotype.
Neoplasm 2
High Grade Tumor VERY_FREQUENT Neoplasm HP:0002664
HER2 Overexpression OBLIGATE Neoplasm HP:0002664
🧬

Genetic Associations

2
ERBB2 (Somatic Amplification)
Somatic
Show evidence (2 references)
PMID:23628726 PARTIAL
"HER2 gene amplification is observed in about 15% of breast cancers."
Abstract reports HER2 amplification frequency in breast cancer.
CIVIC_ASSERTION:2 SUPPORT Other
"HER2 amplification predicts sensitivity to Trastuzumab"
CIViC's accepted assertion supports ERBB2 amplification as the treatment-predictive genetic alteration for trastuzumab response.
PIK3CA (Co-occurring Mutations)
Somatic
💊

Medical Actions

5
Trastuzumab
Action: immunotherapy Ontology label: Immunotherapy NCIT:C15262
Agent: trastuzumab CHEBI:231601
Humanized monoclonal antibody targeting the extracellular domain of HER2. First-line treatment in combination with chemotherapy. Revolutionized HER2+ breast cancer treatment, converting a poor-prognosis subtype into one with excellent outcomes.
Show evidence (1 reference)
CIVIC_ASSERTION:2 SUPPORT Other
"HER2 amplification predicts sensitivity to Trastuzumab"
CIViC's accepted assertion directly supports trastuzumab sensitivity in ERBB2-amplified HER2-positive breast cancer.
Pertuzumab
Action: Pharmacotherapy NCIT:C15986
Agent: pertuzumab NCIT:C38692
Humanized monoclonal antibody that binds HER2 at a different epitope than trastuzumab, preventing HER2 dimerization. Used in combination with trastuzumab and chemotherapy in the neoadjuvant, adjuvant, and metastatic settings.
Trastuzumab Deruxtecan (T-DXd)
Action: immunotherapy Ontology label: Immunotherapy NCIT:C15262
Agent: trastuzumab deruxtecan NCIT:C128799
Antibody-drug conjugate consisting of trastuzumab linked to a topoisomerase I inhibitor payload. Highly effective in HER2+ metastatic breast cancer after prior trastuzumab, and also active in HER2-low breast cancer.
Tucatinib
Action: targeted therapy Ontology label: Targeted Therapy NCIT:C93352
Agent: tucatinib NCIT:C77896
Oral HER2-selective tyrosine kinase inhibitor with activity against brain metastases. Used in combination with trastuzumab and capecitabine in previously treated HER2+ metastatic breast cancer.
Neratinib
Action: targeted therapy Ontology label: Targeted Therapy NCIT:C93352
Agent: neratinib CHEBI:61397
Irreversible pan-HER tyrosine kinase inhibitor. Approved for extended adjuvant therapy after trastuzumab-based treatment and for metastatic disease in combination with capecitabine.
Show evidence (1 reference)
NCIT:C49094 SUPPORT Other
"Neratinib | Accepted_Therapeutic_Use_For | - | - | early stage HER2-overexpressed/amplified breast cancer"
NCI Thesaurus asserts accepted therapeutic use of neratinib for early-stage HER2-overexpressed/amplified breast cancer.
🔬

Biochemical Markers

1
HER2 Testing (IHC and FISH)
{ }

Source YAML

click to show 
name: HER2-Positive Breast Cancer
creation_date: '2026-01-26T02:55:13Z'
updated_date: '2026-05-11T02:45:15Z'
description: >-
  HER2-positive breast cancer is a molecularly-defined subtype of breast cancer
  characterized by amplification or overexpression of the ERBB2 (HER2/neu) gene,
  encoding a receptor tyrosine kinase. HER2 amplification occurs in approximately
  15-20% of breast cancers and historically conferred poor prognosis before the
  advent of HER2-targeted therapies. The development of trastuzumab revolutionized
  treatment and established HER2+ breast cancer as a paradigm for targeted therapy
  in solid tumors. Modern treatment includes multiple HER2-targeted agents including
  monoclonal antibodies, tyrosine kinase inhibitors, and antibody-drug conjugates.
categories:
- Molecularly-Defined Cancer
- Breast Cancer Subtype
- Solid Tumor
parents:
- breast carcinoma
external_assertions:
- name: CIViC ERBB2 amplification trastuzumab sensitivity assertion
  source: CIViC
  assertion_type: accepted_assertion
  external_id: CIVIC_ASSERTION:2
  url: https://civicdb.org/links/assertions/2
  description: >-
    CIViC accepted assertion that ERBB2 amplification in HER2-receptor positive
    breast cancer predicts sensitivity/response to trastuzumab.
  notes: >-
    01-May-2026 CIViC accepted assertion: molecular_profile="ERBB2
    Amplification"; disease="Her2-receptor Positive Breast Cancer";
    assertion_type=Predictive; significance=Sensitivity/Response; therapy=Trastuzumab;
    AMP category=Tier I - Level A.
  evidence:
  - reference: CIVIC_ASSERTION:2
    reference_title: "ERBB2 Amplification / Her2-receptor Positive Breast Cancer (Predictive Sensitivity/Response)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: HER2 amplification predicts sensitivity to Trastuzumab
    explanation: CIViC records an accepted predictive sensitivity assertion for ERBB2 amplification and trastuzumab in HER2-positive breast cancer.
mechanistic_hypotheses:
- hypothesis_group_id: canonical_grb2_rtk_effector_model
  hypothesis_label: Canonical HER2-GRB2 RTK Effector Model
  status: CANONICAL
  description: >-
    Constitutively activated HER2 receptors create phosphotyrosine docking
    sites that recruit GRB2 adaptor complexes, coupling receptor activation to
    canonical RAS-MAPK and PI3K-AKT proliferative signaling. This is the
    textbook HER2+ breast cancer signaling cascade and the explicit
    disease-level instantiation of the rtk_grb2_signaling_adaptation module's
    canonical effector hypothesis.
  evidence:
  - reference: PMID:11175341
    reference_title: Grb2 downregulation leads to Akt inactivation in heregulin-stimulated and ErbB2-overexpressing breast cancer cells.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      the activation of ErbB2 by heregulin or by its overexpression requires
      Grb2 to stimulate the Akt pathway to propagate mitogenic signals
    explanation: >-
      Lim et al. directly demonstrate that GRB2 is required for ErbB2-driven
      Akt activation in heregulin-stimulated and ErbB2-overexpressing breast
      cancer cells — the canonical adaptor function in HER2+ disease.
  - reference: PMID:40289214
    reference_title: GRB2 promotes brain metastasis in HER2-positive breast cancer by regulating the Ras/MAPK pathway.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      GRB2 enhances proliferation, migration, and invasion while suppressing
      apoptosis in HER2-positive breast cancer cells in vitro, primarily by
      regulating phosphorylation and alternative splicing of key proteins
      within the Ras/MAPK pathway.
    explanation: >-
      Wang et al. confirm GRB2's canonical proliferative/MAPK-coupling role
      in HER2+ breast cancer with phenotypic readouts directly attributable
      to GRB2 perturbation.
- hypothesis_group_id: cmtm6_her2_stabilization_resistance_model
  hypothesis_label: CMTM6 HER2 Stabilization Resistance Model
  status: EMERGING
  description: >-
    Trastuzumab resistance is sustained in part by post-translational
    stabilization of the HER2 receptor protein at the cell surface. CMTM6
    (CKLF-like MARVEL transmembrane domain-containing 6) directly interacts
    with HER2 and inhibits HER2 ubiquitination, preserving the GRB2-adaptor
    output even under trastuzumab pressure. Under the interactome-
    rebalancing framing, CMTM6 acts as a separate post-translational pivot
    point in parallel to GRB2 conformational state, and degrading or
    inhibiting CMTM6 may resensitize tumors to HER2-targeted therapy. This
    hypothesis is independent of (and complementary to) GRB2-level
    conformational control.
  evidence:
  - reference: PMID:36627608
    reference_title: CMTM6 overexpression confers trastuzumab resistance in HER2-positive breast cancer.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      these findings highlight that CMTM6 stabilizes HER2 protein,
      contributing to trastuzumab resistance and implicate CMTM6 as a
      potential prognostic marker and therapeutic target for overcoming
      trastuzumab resistance in HER2+ breast cancer
    explanation: >-
      Xu et al. directly establish CMTM6-mediated post-translational HER2
      stabilization as a trastuzumab-resistance mechanism.
  - reference: PMID:36627608
    reference_title: CMTM6 overexpression confers trastuzumab resistance in HER2-positive breast cancer.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      CMTM6 expression was upregulated in trastuzumab-resistant HER2+ breast
      cancer cell
    explanation: >-
      Co-localization, co-immunoprecipitation, and ubiquitination data link
      CMTM6 expression to the trastuzumab-resistant state.
- hypothesis_group_id: grb2_conformational_pivot_resistance_model
  hypothesis_label: GRB2 Conformational Pivot Resistance Model
  status: EMERGING
  description: >-
    GRB2 is a thermodynamic pivot point whose conformational state determines
    whether HER2-driven tumors funnel into cytoplasmic effector dominance,
    nuclear RAD51-dependent replication-fork protection, or PARPi-STING
    innate-immune activation. Allosteric stabilization or PROTAC degradation
    of GRB2 would select between these interactome states and modulate
    trastuzumab/TKI resistance. This hypothesis is distinguishable from the
    canonical effector model by predicting that GRB2 perturbation produces
    different phenotypes depending on which conformational state is locked,
    not simply graded loss of adaptor function.
  evidence:
  - reference: PMID:38459011
    reference_title: GRB2 stabilizes RAD51 at reversed replication forks suppressing genomic instability and innate immunity against cancer.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Growth factor receptor-bound protein 2 (GRB2) is a cytoplasmic adapter
      for tyrosine kinase signaling and a nuclear adapter for
      homology-directed-DNA repair.
    explanation: >-
      Dual cytoplasmic/nuclear GRB2 framing motivates the conformational-pivot
      hypothesis as distinct from the canonical effector model.
  - reference: PMID:38459011
    reference_title: GRB2 stabilizes RAD51 at reversed replication forks suppressing genomic instability and innate immunity against cancer.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In GRB2-depleted cells, PARP inhibitor (PARPi) treatment releases DNA
      fragments from stalled forks into the cytoplasm that activate the
      cGAS-STING pathway to trigger pro-inflammatory cytokine production.
    explanation: >-
      Experimental demonstration that loss of GRB2 fork-protection function
      produces a distinct PARPi-STING vulnerability supports the pivot framing.

pathophysiology:
- name: ERBB2 Gene Amplification
  description: >-
    HER2-positive breast cancer is driven by amplification of the ERBB2 gene on
    chromosome 17q12, resulting in overexpression of the HER2 receptor tyrosine
    kinase. Gene amplification typically results in 25-50 copies per cell, leading
    to massive receptor overexpression on the cell surface.
  evidence:
  - reference: PMID:40303293
    reference_title: "PPARG Activation of Fatty Acid Metabolism Drives Resistance to Anti-HER2 Therapies in HER2-Positive Breast Cancer."
    supports: PARTIAL
    snippet: HER2-positive breast cancer, which accounts for approximately 15-20% of all breast cancers, is characterized by its aggressive recurrence, metastasis and reduced survival.
    explanation: This abstract identifies HER2-positive breast cancer as a distinct, aggressive subtype, supporting the disease definition used here.
  - reference: CIVIC_ASSERTION:2
    reference_title: "ERBB2 Amplification / Her2-receptor Positive Breast Cancer (Predictive Sensitivity/Response)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: HER2 amplification defines a clinically relevant subtype of breast cancer.
    explanation: CIViC's accepted assertion supports ERBB2/HER2 amplification as the defining molecular feature of HER2-positive breast cancer.
  cell_types:
  - preferred_term: luminal epithelial cell of mammary gland
    term:
      id: CL:0002326
      label: luminal epithelial cell of mammary gland
  biological_processes:
  - preferred_term: ERBB2 signaling pathway
    modifier: INCREASED
    term:
      id: GO:0038128
      label: ERBB2 signaling pathway
  downstream:
  - target: Constitutive Receptor Activation
    description: Receptor overexpression leads to ligand-independent dimerization and activation
- name: Constitutive Receptor Activation
  conforms_to: "rtk_grb2_signaling_adaptation#Activated RTK Phosphotyrosine Docking"
  description: >-
    Massive HER2 overexpression promotes spontaneous receptor homodimerization and
    heterodimerization with other ERBB family members (EGFR, HER3, HER4) without
    ligand binding. The phosphorylated receptor tail creates docking sites for SH2-
    domain-containing adaptors including GRB2, instantiating the RTK-phosphotyrosine
    docking trigger of the GRB2 signaling adaptation module.
  biological_processes:
  - preferred_term: transmembrane receptor protein tyrosine kinase signaling pathway
    modifier: INCREASED
    term:
      id: GO:0007169
      label: cell surface receptor protein tyrosine kinase signaling pathway
  - preferred_term: protein autophosphorylation
    modifier: INCREASED
    term:
      id: GO:0046777
      label: protein autophosphorylation
  downstream:
  - target: GRB2 Adaptor Hub
    description: Phosphorylated HER2 recruits GRB2-containing adaptor complexes at pY docking sites.
    evidence:
    - reference: PMID:11175341
      reference_title: Grb2 downregulation leads to Akt inactivation in heregulin-stimulated and ErbB2-overexpressing breast cancer cells.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        the growth factor receptor bound protein-2 (Grb2) is required for the
        proliferation of ErbB2-overexpressing breast cancer cells
      explanation: >-
        Supports the causal link from activated ErbB2/HER2 to engagement of the
        GRB2 adaptor required for ErbB2-driven proliferation.
- name: GRB2 Adaptor Hub
  conforms_to: "rtk_grb2_signaling_adaptation#GRB2 Adaptor Hub"
  description: >-
    GRB2 is the adaptor control point that couples HER2 phosphotyrosine docking
    to downstream effector complexes. In HER2-amplified breast tumors, the GRB2
    adaptor function is constitutively engaged through ERBB2 homo- and
    heterodimers, driving sustained RAS-MAPK and PI3K-AKT signaling. The
    HER2 amplicon at 17q12 frequently co-amplifies GRB7, an SH2 adaptor whose
    expression correlates with GRB2-pathway output and adverse outcome. A
    second, nuclear GRB2 function in RAD51-dependent replication-fork
    protection may rebalance the tumor's interactome toward DNA-damage
    tolerance under HER2-targeted or chemotherapy-induced replication stress.
  genes:
  - preferred_term: GRB2
    term:
      id: hgnc:4566
      label: GRB2
  - preferred_term: GRB7
    term:
      id: hgnc:4567
      label: GRB7
  molecular_functions:
  - preferred_term: growth factor receptor binding
    term:
      id: GO:0070851
      label: growth factor receptor binding
  evidence:
  - reference: PMID:11175341
    reference_title: Grb2 downregulation leads to Akt inactivation in heregulin-stimulated and ErbB2-overexpressing breast cancer cells.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      the growth factor receptor bound protein-2 (Grb2) is required for the
      proliferation of ErbB2-overexpressing breast cancer cells
    explanation: >-
      Lim et al. directly establish GRB2 as a required adaptor for ErbB2-
      driven proliferation in HER2+ breast cancer cells, instantiating the
      module's GRB2 Adaptor Hub node in this disease.
  - reference: PMID:38459011
    reference_title: GRB2 stabilizes RAD51 at reversed replication forks suppressing genomic instability and innate immunity against cancer.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Growth factor receptor-bound protein 2 (GRB2) is a cytoplasmic adapter
      for tyrosine kinase signaling and a nuclear adapter for
      homology-directed-DNA repair.
    explanation: >-
      Establishes the dual cytoplasmic/nuclear GRB2 framing relevant to HER2+
      tumors under replication stress.
  - reference: PMID:23628726
    reference_title: "The HER2 amplicon in breast cancer: Topoisomerase IIA and beyond."
    supports: PARTIAL
    snippet: "HER2 gene amplification is observed in about 15% of breast cancers."
    explanation: >-
      The HER2 amplicon frequently extends to include GRB7, providing a
      structural basis for amplified GRB2-pathway adaptor output in this
      subtype.
  downstream:
  - target: Downstream Oncogenic Signaling
    description: Cytoplasmic GRB2 adaptor complexes activate RAS-MAPK and PI3K-AKT.
    evidence:
    - reference: PMID:11175341
      reference_title: Grb2 downregulation leads to Akt inactivation in heregulin-stimulated and ErbB2-overexpressing breast cancer cells.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        the activation of ErbB2 by heregulin or by its overexpression requires
        Grb2 to stimulate the Akt pathway to propagate mitogenic signals
      explanation: >-
        Supports the causal link from the GRB2 adaptor hub to activation of the
        downstream Akt (PI3K) mitogenic signaling output.
- name: Downstream Oncogenic Signaling
  conforms_to: "rtk_grb2_signaling_adaptation#RAS-MAPK and PI3K-AKT Proliferation Output"
  description: >-
    Activated HER2 signals through PI3K-AKT-mTOR and RAS-RAF-MEK-ERK pathways,
    promoting cell proliferation, survival, and resistance to apoptosis. HER2-HER3
    heterodimers are particularly potent activators of the PI3K pathway. Adaptive
    rewiring of these outputs (rather than HER2 loss) is the dominant resistance
    pattern under trastuzumab and tyrosine kinase inhibition.
  biological_processes:
  - preferred_term: phosphatidylinositol 3-kinase signaling
    modifier: INCREASED
    term:
      id: GO:0043491
      label: phosphatidylinositol 3-kinase/protein kinase B signal transduction
  - preferred_term: MAPK cascade
    modifier: INCREASED
    term:
      id: GO:0000165
      label: MAPK cascade
  evidence:
  - reference: PMID:40289214
    reference_title: GRB2 promotes brain metastasis in HER2-positive breast cancer by regulating the Ras/MAPK pathway.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      GRB2 enhances proliferation, migration, and invasion while suppressing
      apoptosis in HER2-positive breast cancer cells in vitro, primarily by
      regulating phosphorylation and alternative splicing of key proteins
      within the Ras/MAPK pathway.
    explanation: >-
      Documents the Ras/MAPK proliferative and pro-survival output downstream of
      GRB2 in HER2-positive breast cancer cells.
  downstream:
  - target: Uncontrolled Proliferation
    description: Sustained signaling drives tumor growth
    evidence:
    - reference: PMID:40289214
      reference_title: GRB2 promotes brain metastasis in HER2-positive breast cancer by regulating the Ras/MAPK pathway.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        GRB2 enhances proliferation, migration, and invasion while suppressing
        apoptosis in HER2-positive breast cancer cells in vitro, primarily by
        regulating phosphorylation and alternative splicing of key proteins
        within the Ras/MAPK pathway.
      explanation: >-
        Supports the causal link from sustained RAS-MAPK/PI3K signaling to
        enhanced proliferation and suppressed apoptosis.
- name: Uncontrolled Proliferation
  description: >-
    Constitutive HER2 signaling drives continuous cell cycle progression and
    resistance to apoptotic signals. HER2+ tumors are typically high grade with
    high proliferation indices (high Ki-67).
  biological_processes:
  - preferred_term: cell population proliferation
    modifier: INCREASED
    term:
      id: GO:0008283
      label: cell population proliferation
  evidence:
  - reference: PMID:40289214
    reference_title: GRB2 promotes brain metastasis in HER2-positive breast cancer by regulating the Ras/MAPK pathway.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      GRB2 enhances proliferation, migration, and invasion while suppressing
      apoptosis in HER2-positive breast cancer cells in vitro, primarily by
      regulating phosphorylation and alternative splicing of key proteins
      within the Ras/MAPK pathway.
    explanation: >-
      Documents enhanced proliferation and suppressed apoptosis in HER2-positive
      breast cancer cells driven by sustained Ras/MAPK signaling.
histopathology:
- name: Invasive Ductal Carcinoma
  finding_term:
    preferred_term: Invasive Breast Carcinoma of No Special Type
    term:
      id: NCIT:C4194
      label: Invasive Breast Carcinoma of No Special Type
  frequency: VERY_FREQUENT
  description: Invasive ductal carcinoma is the most common type of breast cancer.
  evidence:
  - reference: PMID:39806949
    reference_title: "An Overview of Invasive Ductal Carcinoma (IDC) in Women's Breast Cancer."
    supports: PARTIAL
    snippet: "Invasive ductal carcinoma (IDC) is the most common type of breast cancer,"
    explanation: Abstract states that invasive ductal carcinoma is the most common breast cancer type.

phenotypes:
- category: Neoplastic
  name: Breast Carcinoma
  frequency: OBLIGATE
  diagnostic: true
  description: >-
    HER2-positive breast cancers are typically invasive ductal carcinomas of
    high histologic grade. They often present as palpable masses or are detected
    on screening mammography.
  phenotype_term:
    preferred_term: Breast carcinoma
    term:
      id: HP:0003002
      label: Breast carcinoma
  evidence:
  - reference: PMID:39806949
    reference_title: "An Overview of Invasive Ductal Carcinoma (IDC) in Women's Breast Cancer."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Invasive ductal carcinoma (IDC) is the most common type of breast cancer,"
    explanation: >-
      HER2-positive tumors are typically invasive ductal (breast) carcinomas,
      supporting breast carcinoma as the defining neoplastic phenotype.
- category: Histopathologic
  name: High Grade Tumor
  frequency: VERY_FREQUENT
  description: >-
    HER2+ breast cancers are predominantly high grade (grade 2-3) with high
    mitotic rates and nuclear pleomorphism.
  phenotype_term:
    preferred_term: Neoplasm
    term:
      id: HP:0002664
      label: Neoplasm
- category: Molecular
  name: HER2 Overexpression
  frequency: OBLIGATE
  diagnostic: true
  description: >-
    Defining feature is HER2 protein overexpression (IHC 3+) or gene amplification
    (FISH HER2/CEP17 ratio ≥2.0 or HER2 copy number ≥6). IHC 2+ requires reflex
    FISH testing for confirmation.
  phenotype_term:
    preferred_term: Neoplasm
    term:
      id: HP:0002664
      label: Neoplasm
biochemical:
- name: HER2 Testing (IHC and FISH)
  notes: >-
    HER2 status is determined by immunohistochemistry (IHC) for protein expression
    and/or fluorescence in situ hybridization (FISH) for gene amplification. IHC
    scores of 0-1+ are negative, 2+ is equivocal (requires FISH), and 3+ is positive.
    FISH positive is defined as HER2/CEP17 ratio ≥2.0 or average HER2 copy number ≥6.
genetic:
- name: ERBB2
  association: Somatic Amplification
  inheritance:
  - name: Somatic
  notes: >-
    ERBB2 (17q12) encodes the HER2 receptor tyrosine kinase. Amplification occurs
    somatically and is not inherited. The amplicon often includes neighboring genes
    including GRB7 and TOP2A. Amplification level correlates with HER2 protein
    expression and response to HER2-targeted therapy.
  evidence:
  - reference: PMID:23628726
    reference_title: "The HER2 amplicon in breast cancer: Topoisomerase IIA and beyond."
    supports: PARTIAL
    snippet: "HER2 gene amplification is observed in about 15% of breast cancers."
    explanation: "Abstract reports HER2 amplification frequency in breast cancer."
  - reference: CIVIC_ASSERTION:2
    reference_title: "ERBB2 Amplification / Her2-receptor Positive Breast Cancer (Predictive Sensitivity/Response)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: HER2 amplification predicts sensitivity to Trastuzumab
    explanation: CIViC's accepted assertion supports ERBB2 amplification as the treatment-predictive genetic alteration for trastuzumab response.
- name: PIK3CA
  association: Co-occurring Mutations
  inheritance:
  - name: Somatic
  notes: >-
    PIK3CA mutations occur in approximately 30% of HER2+ breast cancers and may
    confer resistance to HER2-targeted therapy. Testing is recommended for
    treatment selection (alpelisib in ER+/HER2+ cases).
treatments:
- name: Trastuzumab
  description: >-
    Humanized monoclonal antibody targeting the extracellular domain of HER2.
    First-line treatment in combination with chemotherapy. Revolutionized
    HER2+ breast cancer treatment, converting a poor-prognosis subtype into
    one with excellent outcomes.
  treatment_term:
    preferred_term: immunotherapy
    term:
      id: NCIT:C15262
      label: Immunotherapy
    therapeutic_agent:
    - preferred_term: trastuzumab
      term:
        id: CHEBI:231601
        label: trastuzumab
  evidence:
  - reference: CIVIC_ASSERTION:2
    reference_title: "ERBB2 Amplification / Her2-receptor Positive Breast Cancer (Predictive Sensitivity/Response)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: HER2 amplification predicts sensitivity to Trastuzumab
    explanation: CIViC's accepted assertion directly supports trastuzumab sensitivity in ERBB2-amplified HER2-positive breast cancer.
- name: Pertuzumab
  description: >-
    Humanized monoclonal antibody that binds HER2 at a different epitope than
    trastuzumab, preventing HER2 dimerization. Used in combination with
    trastuzumab and chemotherapy in the neoadjuvant, adjuvant, and metastatic
    settings.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: pertuzumab
      term:
        id: NCIT:C38692
        label: Pertuzumab
- name: Trastuzumab Deruxtecan (T-DXd)
  description: >-
    Antibody-drug conjugate consisting of trastuzumab linked to a topoisomerase I
    inhibitor payload. Highly effective in HER2+ metastatic breast cancer after
    prior trastuzumab, and also active in HER2-low breast cancer.
  treatment_term:
    preferred_term: immunotherapy
    term:
      id: NCIT:C15262
      label: Immunotherapy
    therapeutic_agent:
    - preferred_term: trastuzumab deruxtecan
      term:
        id: NCIT:C128799
        label: Trastuzumab Deruxtecan
- name: Tucatinib
  description: >-
    Oral HER2-selective tyrosine kinase inhibitor with activity against brain
    metastases. Used in combination with trastuzumab and capecitabine in
    previously treated HER2+ metastatic breast cancer.
  treatment_term:
    preferred_term: targeted therapy
    term:
      id: NCIT:C93352
      label: Targeted Therapy
    therapeutic_agent:
    - preferred_term: tucatinib
      term:
        id: NCIT:C77896
        label: Tucatinib
- name: Neratinib
  description: >-
    Irreversible pan-HER tyrosine kinase inhibitor. Approved for extended
    adjuvant therapy after trastuzumab-based treatment and for metastatic
    disease in combination with capecitabine.
  treatment_term:
    preferred_term: targeted therapy
    term:
      id: NCIT:C93352
      label: Targeted Therapy
    therapeutic_agent:
    - preferred_term: neratinib
      term:
        id: CHEBI:61397
        label: neratinib
  evidence:
  - reference: NCIT:C49094
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Neratinib | Accepted_Therapeutic_Use_For | - | - | early stage HER2-overexpressed/amplified breast cancer"
    explanation: >-
      NCI Thesaurus asserts accepted therapeutic use of neratinib for early-stage
      HER2-overexpressed/amplified breast cancer.
discussions:
- discussion_id: gap_her2_grb2_adaptor_pivot
  prompt: >-
    Is the GRB2 adaptor hub a tractable allosteric pivot point for rebalancing
    the HER2+ breast cancer interactome under HER2-targeted therapy resistance,
    and does conformational control of GRB2 (versus its degradation) change
    which adaptive bypass routes the tumor recruits?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#GRB2 Adaptor Hub
  - pathophysiology#Downstream Oncogenic Signaling
  rationale: >-
    HER2-targeted antibodies and TKIs do not eliminate downstream GRB2 adaptor
    output: resistant tumors typically rewire RAS-MAPK and PI3K-AKT signaling
    rather than lose HER2. GRB2 also has a documented nuclear RAD51 fork-
    protection role under replication stress. Treating GRB2 as a thermodynamic
    pivot — stabilizing distinct SH2/SH3 conformational states with allosteric
    binders, or degrading the protein with PROTAC warheads — would let us test
    whether different perturbations funnel the interactome into distinct
    pathological survival states (cytoplasmic effector dominance vs. nuclear
    fork-protection dominance vs. innate-immune activation through PARPi-
    induced cytosolic DNA).
  proposed_experiments:
  - experiment_id: exp_her2_grb2_conformational_pivot
    name: Allosteric GRB2 stabilization versus PROTAC degradation in HER2+ organoids
    description: >-
      Treat HER2-amplified patient-derived breast cancer organoids and isogenic
      cell-line panels (HER2-amplified, HER2-amplified plus PIK3CA-mutant,
      trastuzumab-resistant derivatives) with (a) allosteric GRB2 SH2/SH3
      binders tuned to stabilize discrete conformational states, (b) a GRB2-
      directed PROTAC warhead that physically degrades the adaptor, and (c)
      paired HER2 inhibition (trastuzumab, tucatinib, T-DXd). Read out RAS-
      MAPK and PI3K-AKT effector signaling, nuclear GRB2 localization, RAD51
      fork-protection at stalled replication forks, cytosolic DNA release,
      cGAS-STING activation, and immune-cell killing in autologous co-culture.
      Compare to PARP-inhibitor co-treatment arms to test whether GRB2 pivot
      state predicts PARPi-STING vulnerability.
    experiment_type:
      preferred_term: controlled perturbation experiment
    model_systems:
    - name: HER2-amplified patient-derived breast cancer organoid panel
      description: >-
        Matched patient-derived organoids spanning trastuzumab-naive,
        trastuzumab-resistant, and PIK3CA-co-mutant HER2+ disease, paired with
        autologous immune cells for co-culture readouts.
      experimental_model_type: ORGANOID
      organism:
        preferred_term: human
        term:
          id: NCBITaxon:9606
          label: Homo sapiens
      tissue_term:
        preferred_term: mammary gland
        term:
          id: UBERON:0001911
          label: mammary gland
      cell_types:
      - preferred_term: luminal epithelial cell of mammary gland
        term:
          id: CL:0002326
          label: luminal epithelial cell of mammary gland
    perturbations:
    - name: Allosteric GRB2 conformational stabilization
      target: pathophysiology#GRB2 Adaptor Hub
      description: >-
        Small-molecule allosteric binders tuned to stabilize distinct SH2/SH3
        conformational states of GRB2 to test conformation-specific output.
      genes:
      - preferred_term: GRB2
        term:
          id: hgnc:4566
          label: GRB2
    - name: GRB2 PROTAC degradation
      target: pathophysiology#GRB2 Adaptor Hub
      description: >-
        Targeted GRB2 degradation via PROTAC warhead to compare adaptor loss
        with adaptor conformational locking.
      genes:
      - preferred_term: GRB2
        term:
          id: hgnc:4566
          label: GRB2
      effect: DECREASED
    - name: PARP inhibitor replication-stress challenge
      target: pathophysiology#GRB2 Adaptor Hub
      description: >-
        Co-administer PARP inhibitor to test whether GRB2 conformational state
        gates PARPi-induced cytosolic DNA and cGAS-STING activation.
    readouts:
    - name: RAS-MAPK and PI3K-AKT effector output
      target: pathophysiology#Downstream Oncogenic Signaling
      biological_processes:
      - preferred_term: MAPK cascade
        term:
          id: GO:0000165
          label: MAPK cascade
      direction: POSITIVE
    - name: Nuclear GRB2 / RAD51 fork-protection and innate-immune activation
      target: pathophysiology#GRB2 Adaptor Hub
      biological_processes:
      - preferred_term: DNA damage response
        term:
          id: GO:0006974
          label: DNA damage response
      - preferred_term: innate immune response
        term:
          id: GO:0045087
          label: innate immune response
      direction: NEGATIVE
      interpretation: >-
        Loss of nuclear GRB2 / RAD51 fork-protection together with increased
        innate-immune activation under PARP inhibition would support a
        conformation-gated state switch.
    decision_criterion: >-
      The conformational pivot model is supported if allosteric stabilization
      and PROTAC degradation produce distinct effector versus DDR phenotypes
      in matched HER2+ models, and if at least one perturbation sensitizes
      trastuzumab-resistant lines to PARP-inhibitor-driven cytosolic DNA and
      cGAS-STING activation.
    would_support:
    - pathophysiology#GRB2 Adaptor Hub
    - pathophysiology#Downstream Oncogenic Signaling
    evidence:
    - reference: PMID:38459011
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        In GRB2-depleted cells, PARP inhibitor (PARPi) treatment releases DNA
        fragments from stalled forks into the cytoplasm that activate the
        cGAS-STING pathway to trigger pro-inflammatory cytokine production.
      explanation: >-
        Provides the experimental precedent for GRB2 perturbation plus PARP
        inhibition producing cytosolic DNA and innate immune activation, which
        the HER2+ experiment generalizes to a conformational-pivot framing.

disease_term:
  preferred_term: HER2 positive breast carcinoma
  term:
    id: MONDO:0006244
    label: HER2 positive breast carcinoma

classifications:
  icdo_morphology:
    classification_value: Adenocarcinoma
    evidence:
    - reference: PMID:39806949
      reference_title: "An Overview of Invasive Ductal Carcinoma (IDC) in Women's Breast Cancer."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Invasive ductal carcinoma (IDC) is the most common type of breast cancer,"
      explanation: HER2-positive breast cancers are predominantly invasive ductal (adeno)carcinomas, supporting the ICD-O adenocarcinoma morphology assignment.
  harrisons_chapter:
  - classification_value: ONCOLOGY_HEMATOLOGY
    evidence:
    - reference: PMID:39806949
      reference_title: "An Overview of Invasive Ductal Carcinoma (IDC) in Women's Breast Cancer."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Invasive ductal carcinoma (IDC) is the most common type of breast cancer,"
      explanation: Breast carcinoma is an oncologic malignancy, supporting the Harrison's Oncology and Hematology classification.
📚

References & Deep Research

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Asta Literature Retrieval: Pathophysiology and clinical mechanisms of HER2-Positive Breast Cancer. Core disease mechanisms, molecular and cellul...
Asta Scientific Corpus Retrieval 18 citations 2026-05-26T23:06:35.606200

Asta Literature Retrieval: Pathophysiology and clinical mechanisms of HER2-Positive Breast Cancer. Core disease mechanisms, molecular and cellul...

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  • Papers retrieved: 18
  • Snippets retrieved: 20

Relevant Papers

[1] Resistance and Overcoming Resistance in Breast Cancer

  • Authors: Andrea Luque-Bolivar, E. Pérez-Mora, V. Villegas, Milena Rondón-Lagos
  • Year: 2020
  • Venue: Breast Cancer : Targets and Therapy
  • URL: https://www.semanticscholar.org/paper/8cf9a7b648985175a9f0f35ca0bdc8a2889359a9
  • DOI: 10.2147/BCTT.S270799
  • PMID: 33204149
  • PMCID: 7666993
  • Citations: 108
  • Summary: This review is focused on recent studies on the possible biological and molecular mechanisms involved in both response and resistance to treatment in BC and emerging treatments that seek to overcome resistance and reduce side effects.
  • Evidence snippets:
  • Snippet 1 (score: 0.533) > Cancer is a common disease and represents one of the biggest health problems in the world and a significant global concern. The incidence and mortality rates of breast cancer (BC) have increased in recent years, and BC is currently the leading cause of cancer death in women worldwide. 1 Decision making for the treatment of patients with BC is primarily based on the assessment of clinical and pathological parameters. In particular, the immunohistochemical evaluation of prognostic factors, such as estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor 2 (HER2) are critical for tumor subtype classification and histological grade, which play an important role in determining therapeutic strategies. For example, patients with ER-positive (ER+) tumors receive endocrine therapy, and a small fraction of these patients also receive chemotherapy. Patients with HER2-positive tumors (HER2 enriched or HER2+) are treated with antibodies directed against HER2 or small-molecule inhibitors in combination with chemotherapy. ][4] BC is a heterogeneous and complex disease in which each patient has unique morphological and molecular features, rather than a disease in which only a few genes, proteins, and/or signaling pathways contribute to disease progression in a simple, independent, and autonomous manner. Studies have shown that patients with the same type of BC can show differential responses to treatment, which further indicates the high heterogeneity in this disease. Despite the great technological advances that have enhanced our understanding of human cancers as heterogeneous diseases, current clinicopathological and molecular parameters leave a significant number of patients at risk of over-treatment and side effects. > Currently, drug-resistant BC is treated by selecting other drugs, without understanding the molecular mechanisms involved in the resistance of a given case. Better understanding of the mechanisms involved in the development of resistance might not only reduce the adverse effects of treatment but also lead to the development of new strategies for improving diagnosis and prognosis and achieving a better response to therapy. This review focuses on recent studies on the biological and molecular mechanisms of response and resistance to treatment in BC.

[2] Circulating metabolites serve as diagnostic biomarkers for HER2‐positive breast cancer and have predictive value for trastuzumab therapy outcomes

  • Authors: Changfei Mao, Min Wang, Li Li, Jin-hai Tang
  • Year: 2022
  • Venue: Journal of Clinical Laboratory Analysis
  • URL: https://www.semanticscholar.org/paper/c170d9b1deaced83d0f44f9f270bbfa9a81949e0
  • DOI: 10.1002/jcla.24212
  • PMID: 34994982
  • PMCID: 8842188
  • Citations: 14
  • Influential citations: 1
  • Summary: S serum‐based metabolic biomarkers for diagnosis of HER2‐positive breast cancers and predicts the therapeutic effects of trastuzumab therapy are developed.
  • Evidence snippets:
  • Snippet 1 (score: 0.507) > The overall goal of this study was to delineate the unique serum metabolic biomarkers of HER2-positive breast cancer patients. By using the UPLC-TOF-MS method platform to analyze the serum samples of 20 women with HER2-positive breast cancer and 30 normal women in the control group, we detected a series of significantly changed metabolites that were associated with HER2-positive breast cancer, covering a wide range of metabolic classes. Finally, from archived trastuzumab response data from HER2-positive breast cancer patients, we discovered 2 metabolites and developed a risk score that can predict trastuzumab resistance status. Through comprehensive data interpretation, we acquired a better understanding of the metabolic features in HER2-positive breast cancer and trastuzumab therapy status. > The emergence of omics methods is effectively accelerating predictive, treating and personalized therapeutics. 9 Metabolites more directly reflect and are linked closer to the phenotype of the pathology than genes and proteins. 10 Focusing on metabolite differences and the discovery of characteristic metabolites can be a shortcut and supplement the gene and protein level omics methods, and could also efficiently explain the mechanisms underlying various phenotypic variations. Thus, metabolomics screening is considered to be an effective, money-saving, and noninvasive option. > Each breast cancer subtype has inherent molecular features and metastatic potential, and its natural heterogeneity results in a high degree of difference in prognosis and the clinical response to available drugs, even for patients with a similar diagnosis, histology, and disease stages. 11 Therefore, accurate determination of the molecular subtype of breast cancer is very important for personalized treatment. In fact, there is evidence that compared with patients with mismatched therapies, patients who receive the correct molecularly matched therapy have a higher overall response rate, less treatment failure, and higher survival rates. 12 Clinically, liquid biopsy procedures and subsequent histopathological analysis are usually used to study the molecular and genetic information of cancer cells to diagnose and differentiate breast cancer and classify it into subtypes. 13 is analysis technique is invasive and time-consuming.
  • Snippet 2 (score: 0.474) > its application. 3,4 However, there are no known diagnostic biomarkers to improve the early diagnosis of HER2-positive breast cancer and the clinical utility of trastuzumab therapy. > Cancer-related liquid biopsy biomarkers can demonstrate the occurrence, progression and prognosis of cancers and are of great value for the early diagnosis of cancers, prediction of treatment response, and prognostic monitoring. 5 Metabolomics has emerged as a powerful analytical tool to provide new discoveries, and modern analysis methods are being used to study metabolic biomarkers related to diseases for clinical applications and to detect their abnormal changes in the living body. 6 As active modulators of gene and protein activity, metabolites have been widely adopted to investigate metabolic mechanisms underlying cancer occurrence, to evaluate treatment efficacy and monitor the prognosis to provide new diagnostic ideas and guide the development of better therapeutic strategies. 7 However, to the authors' knowledge, untargeted metabolomic investigation of serum metabolites has not been thoroughly conducted. > In our work, we used ultrahigh-performance liquid time of flight mass spectrometry (UPLC-TOF-MS)-based serum metabolomics and multivariate statistical analysis to investigate the circulating metabolite profiling of HER2-positive breast cancer. L-arginine and arachidonic acid were elevated in trastuzumab-responsive and trastuzumab-resistant HER2-positive breast cancer patients, and increased until reaching their peaks in trastuzumab-resistant HER2positive breast cancer patients. Moreover, an equation for assessing the risk scores based on linear logistic regression models involving L-arginine and arachidonic acid was created, which was beneficial for revealing metabolic changes in HER2-positive breast cancer and enhancing current trastuzumab-based therapy. These unique circulating metabolites in serum not only uncover the molecular characteristics of HER2-positive breast cancer patients but also enable personalized therapy.

[3] Determining the Factors Predicting the Response to Anti-HER2 Therapy in HER2-Positive Breast Cancer Patients

  • Authors: Jinshan You, K. Park, Eun Sook Lee, Y. Kwon, Kyoungsook Kim et al.
  • Year: 2021
  • Venue: Cancer Control : Journal of the Moffitt Cancer Center
  • URL: https://www.semanticscholar.org/paper/41207408a25f78de91d31876a037ff6f63afe2dd
  • DOI: 10.1177/10732748221141672
  • PMID: 36814068
  • PMCID: 9950611
  • Citations: 1
  • Summary: This multigene assay-based study provides insights into breast cancer signaling and possible predictions of therapeutic response to targeted therapies such as trastuzumab.
  • Evidence snippets:
  • Snippet 1 (score: 0.507) > We found that expression changes in 34 genes in several pathways were related to the response to trastuzumabcontaining treatment in HER2-type breast cancer, interfered with adhesion to other cells or tissues (focal adhesion), and regulated ECM-receptor interactions and phagosome action. As a result, the decreased tumor invasiveness and enhanced drug effects might be considered as a potential mechanism for better drug response in the CR group. Of note, functional pathway analysis showed that these pathways affect the HER2 response by interacting with the PI3K pathway and the MAP kinase pathway. As previously reported by Toomey et al and other investigators, high activation of the PI3K pathway is associated with poor response to anti-HER2 therapy in HER2positive breast cancer patients. 12 Neoadjuvant chemotherapy (NAC) is used in the context of locally advanced breast cancer to lower the staging of the tumor, improve operability, and increase the chances of breastconserving surgery. 13,14 Patients receiving NAC share equivalent disease progression and overall survival as patients receiving postoperative chemotherapy alone. 15 Currently, Trastuzumab is a HER2-targeted therapy approved by the United States Food and Drug Administration for HER2positive breast cancer in neoadjuvant, adjuvant, and metastatic settings. Since 2013, Korean health insurance coverage for trastuzumab has expanded to the neoadjuvant setting; hence, the number of patients who can undergo this treatment has increased. Neoadjuvant therapy is administered before surgery, and it is important to predict the treatment response. > Achieving pCR with neoadjuvant anti-HER2 targeted chemotherapy is a crude surrogate for long-term survival of patients with HER2-positive breast cancer. Hou et al demonstrated that HER2 intratumoral heterogeneity is associated with an incomplete response to anti-HER2 neoadjuvant chemotherapy. 16 Our study suggested that genes that are unique to HER2 and related to this HER2 intratumoral heterogeneity are associated with the functional pathways for cell signaling, such as the cell cycle and cell structure. Nahta et al reported that cell signaling pathways were related to a mechanism underlying resistance to HER2-targeted therapy in human breast cancer. 4 This can be in

[4] Immune Effects of Transtuzumab in HER2 Positive Breast Cancer

  • Authors: A. Zgura, L. Galeș, B. Haineala, E. Brătilă, C. Mehedințu et al.
  • Year: 2019
  • Venue: Revista de Chimie
  • URL: https://www.semanticscholar.org/paper/e8a43325891084c3abce704239aacecfc11ae542
  • DOI: 10.37358/rc.19.8.7428
  • Summary: The results of a study that included 22 patients diagnosed with Her2 positive breast cancer undergoing treatment with Transtuzumab are presented, finding that the drug induces antibody-dependant cell-mediated cytotoxicity.
  • Evidence snippets:
  • Snippet 1 (score: 0.505) > Breast cancer is a multifactorial disease in which the key mechanisms of cellular function are implicated, involving molecules of different biochemical classes, functions and types: hormones, growth factors, receptors, signalling pathways, proteases, chromosomal genes, and specific molecules of ribonucleic acids [1][2]. Each of these factors represents a direct therapeutic target, describing a new era in the cancer therapy-molecular biological therapy [3]. > The human epidermal growth factor receptor (EGFR) family comprises four transmembrane receptors, which are involved in the signal transduction pathways regulating cell growth and differentiation: EGFR/HER1, c-erbB2/HER2, HER3, and HER4 [2,3]. Breast cancers overexpressing the human epidermal growth factor receptors, HER1 (EGFR/ c-erbB-1) or HER2 (neu-c-erbB-2), have been associated with disease progression, survival, stage and treatment response [4]. HER2 expression in breast cancer tissue is indicative of an aggressive pathology and it is considered a marker of poor prognosis. > The development of trastuzumab and lapatinib has improved the way for women with HER2-positive disease [5][6]. > The targeted therapy of Trastuzumab represents the standard treatment for breast cancer patients with HER2 positive [7]. There has been increasing evidence that the immune system plays a significant role in the therapeutic effects of HER2-targeted therapy [8].

[5] Construction of a human epidermal growth factor receptor 2-related gene risk model for predicting breast cancer prognosis

  • Authors: Limin Huang, Chunhong Xu, Yining Song, F. Sun, Xuemei Sun et al.
  • Year: 2025
  • Venue: Oncology Letters
  • URL: https://www.semanticscholar.org/paper/10d68928636e88ffc221bc3d48135d918831b1a8
  • DOI: 10.3892/ol.2025.15414
  • PMID: 41383978
  • PMCID: 12690547
  • Summary: It was found that patients in the high-risk group had significantly shorter survival times than those in the low-risk group, and a nomogram, incorporating risk groups and clinicopathological features, demonstrated strong predictive ability and high accuracy.
  • Evidence snippets:
  • Snippet 1 (score: 0.499) > Therefore, in the present study, the molecular mechanisms of the key gene ELOVL2 in HER2-positive breast cancer were preliminarily explored. The results showed that ELOVL2 overexpression inhibited the proliferation of HER2-positive breast cancer cells by inhibiting the PI3K-AKT pathway, suggesting that ELOVL2 is a potential target gene for the treatment of patients with HER2-positive breast cancer, laying the foundation for targeted therapy and improving the clinical adaptability of this model. > However, the current study has several limitations. First, the small sample size may have affected the accuracy of the results. Second, the molecular mechanisms of key genes affecting the prognosis of patients with HER2-positive breast cancer require further exploration. Third, the screened drugs must be validated experimentally. Therefore, future studies should collect additional cases, include a larger number of clinical samples, and conduct relevant clinical studies to provide effective personalized treatment plans or targeted therapies for patients and to improve their prognosis. > In conclusion, a valuable prognostic model that included eight HER2-related genes was developed in the current study. This model could accurately evaluate the survival rate of patients with HER2-positive breast cancer, and provide effective indicators or therapeutic targets for HER2-positive breast cancer. The present findings provide a new direction for the development of novel immunotherapeutic targets and personalized treatment for HER2-positive breast cancer.

[6] Targeted Therapeutic Options and Future Perspectives for HER2-Positive Breast Cancer

  • Authors: A. Ferrando-Díez, E. Felip, A. Pous, Milana Bergamino Sirvén, M. Margelí
  • Year: 2022
  • Venue: Cancers
  • URL: https://www.semanticscholar.org/paper/400fa20871992d6e43674daf76cd66ca0515696a
  • DOI: 10.3390/cancers14143305
  • PMID: 35884366
  • PMCID: 9320771
  • Citations: 36
  • Summary: The milestones that have had an impact on this disease up to their implementation in clinical practice are intended to understand and the role that modulation of the immune response might play in treatment and prognosis is focused on.
  • Evidence snippets:
  • Snippet 1 (score: 0.497) > Simple Summary The development of several antiHuman Epidermal Growth Factor Receptor 2 (HER2) treatments over the last few years has improved the landscape of HER2-positive breast cancer. Despite this, relapse is still the main issue in HER2-positive breast cancer. The reasons for therapeutic failure lie in the heterogeneity of the disease itself, as well as in the drug resistance mechanisms. In this review, we intended to understand the milestones that have had an impact on this disease up to their implementation in clinical practice. In addition, understanding the underlying molecular biology of HER2-positive disease is essential for the optimization and personalization of the different treatment options. For this reason, we focused on two relevant aspects, which are triple-positive disease and the role that modulation of the immune response might play in treatment and prognosis. Abstract Despite the improvement achieved by the introduction of HER2-targeted therapy, up to 25% of early human epidermal growth factor receptor 2-positive (HER2+) breast cancer (BC) patients will relapse. Beyond trastuzumab, other agents approved for early HER2+ BC include the monoclonal antibody pertuzumab, the antibody-drug conjugate (ADC) trastuzumab-emtansine (T-DM1) and the reversible HER2 inhibitor lapatinib. New agents, such as trastuzumab-deruxtecan or tucatinib in combination with capecitabine and trastuzumab, have also shown a significant improvement in the metastatic setting. Other therapeutic strategies to overcome treatment resistance have been explored in HER2+ BC, mainly in HER2+ that also overexpress estrogen receptors (ER+). In ER+ HER2+ patients, target therapies such as phosphoinositide-3-kinase (PI3K) pathway inhibition or cyclin-dependent kinases 4/6 blocking may be effective in controlling downstream of HER2 and many of the cellular pathways associated with resistance to HER2-targeted therapies. Multiple trials have explored these strategies with some promising results, and probably, in the next years conclusive results will succeed. In addition, HER2+ BC is known to be more immun

[7] Partial Response to Pyrotinib Plus Capecitabine in an Advanced Breast Cancer Patient with HER2 Amplification and R157W Mutation After Anti-HER2 Treatment: A Case Report and Literature Review

  • Authors: Yan-chun Qu, Yufeng Liu, Kailin Ding, Yong Li, Xiaoyu Hong et al.
  • Year: 2021
  • Venue: OncoTargets and therapy
  • URL: https://www.semanticscholar.org/paper/f9585f092f5e6fad50f311e227b947fcad414b1d
  • DOI: 10.2147/OTT.S289876
  • PMID: 33688205
  • PMCID: 7936716
  • Citations: 3
  • Summary: The small-molecule pan-HER family irreversible inhibitor pyrotinib combined with capecitabine has shown a promising effect in the treatment of HER2 mutation-induced resistance, but the molecular mechanism and efficacy need to be further verified.
  • Evidence snippets:
  • Snippet 1 (score: 0.495) > apatinib has achieved certain clinical efficacy in metastatic HER2-positive breast cancer treated with trastuzumab, but a significant proportion of patients develop disease progression due to innate or acquired resistance to lapatinib. 24,25 Studies on the molecular mechanisms of trastuzumab and lapatinib resistance 26 found that overexpression of other HER family receptors and their ligands, loss of PTEN leading to activation of the PI3K/Akt/mTOR pathway, PI3KCA mutation, and Akt mutation or amplification were common causes of drug resistance. Drug resistance has become an urgent problem. > The patient developed resistance to lapatinib combined with trastuzumab. The HER2 gene mutation was not detected before the patient received lapatinib plus trastuzumab treatment, while the R157W mutation was found in the disease progression after treatment. Moreover, by comparing the two gene test results (Table 1), only the HER2 mutation was acquired, so it was believed that the HER2 mutation was the main mechanism of drug resistance in this case. In recent years, with the gradual deepening of the understanding of HER2, it is believed that HER2 mutation plays an important role in the incidence, development and resistance of breast cancer. 27,28 The primary HER2 mutation mostly occurred in HER2 negative conditions, while in HER2 positive breast cancer the HER2 mutation mostly occurred after anti-HER2 treatment. Fang et al 6 performed HER2 full-length gene sequencing on the tissues of 198 patients with metastatic breast cancer (MBC) after multiple cycles of treatment and found that the rate of HER2 mutations in patients treated with trastuzumab was as high as 17.7%. Park et al 7 also carried out NGS tests on the tissues of 36 refractory MBC patients after multi-cycle and multi-drug treatment, and found that 5 out of 6 patients with HER2 mutation were HER2 positive and developed drug resistance after receiving anti-HER2 drugs (trastuzumab, lapatinib).

[8] A Decade of Innovation in Breast Cancer (2015–2025): A Comprehensive Review of Clinical Trials, Targeted Therapies and Molecular Perspectives

  • Authors: Klaudia Dynarowicz, D. Bartusik-Aebisher, Sara Czech, A. Kawczyk-Krupka, D. Aebisher
  • Year: 2026
  • Venue: Cancers
  • URL: https://www.semanticscholar.org/paper/00d888cd7d78bd5c497ea7ad83fb06be53f0b6f3
  • DOI: 10.3390/cancers18030361
  • PMID: 41681834
  • PMCID: 12897389
  • Citations: 1
  • Summary: This review summarizes the major progress made between 2015 and 2025 across all main types of breast cancer, including modern hormone therapies, drugs that block key growth pathways, treatments directed at the Human Epidermal Growth Factor Receptor 2 (HER2) protein, immunotherapies, antibody–drug conjugates, as well as emerging and primarily adjunctive photodynamic approaches.
  • Evidence snippets:
  • Snippet 1 (score: 0.491) > Hormone receptor-positive/HER2-negative (HR+/HER2−) breast cancer is the most common biological subtype, accounting for approximately 70% of all cases [28]. Its development and maintenance are closely linked to the activity of the estrogen receptor (ER) and the progesterone receptor (PR), which regulate the expression of numerous genes involved in proliferation, differentiation, and survival of mammary epithelial cells [29]. Activation of ER increases the expression of cyclin D1, initiating the formation of CDK4/6-cyclin D complexes. These complexes subsequently phosphorylate the retinoblastoma (RB) protein, releasing its inhibitory effect on the E2F transcription factor and enabling the G1-S phase transition of the cell cycle [30]. Deregulation of this mechanism results in excessive cellular proliferation and loss of cell-cycle control, representing one of the fundamental pathogenic processes in HR-positive breast cancer [31]. The HR+/HER2−subtype is typically characterized by slower disease progression and a strong dependence on hormonal signaling, which makes it particularly responsive to endocrine therapy. Over time, however, endocrine resistance may emerge, driven by mechanisms such as ESR1 mutations, activation of the PI3K/AKT/mTOR pathway, or other adaptive cellular processes [32,33]. The intricate interplay between hormonal, proliferative, and molecular signaling pathways positions HR+/HER2− breast cancer as a quintessential example of a tumor in which underlying biological processes directly dictate therapeutic responsiveness.

[9] Screening and Identification of Key Biomarkers in Acquired Lapatinib-Resistant Breast Cancer

  • Authors: S. Bao, Yi Chen, Fan Yang, Chunxiao Sun, Mengzhu Yang et al.
  • Year: 2020
  • Venue: Frontiers in Pharmacology
  • URL: https://www.semanticscholar.org/paper/ce98e91310c373596010ed74698f9a7ae34f3cde
  • DOI: 10.3389/fphar.2020.577150
  • PMID: 33013420
  • PMCID: 7500445
  • Citations: 8
  • Summary: Hub genes are involved in the complex mechanisms underlying AlR in breast cancer and provide favorable support for treatment of ALR in future, according to analysis of seven hub genes.
  • Evidence snippets:
  • Snippet 1 (score: 0.483) > Based on molecular markers, breast cancer is divided into four subgroups: luminal A, luminal B, basal-like, and human epidermal growth factor receptor 2 (HER2)-enriched (Perou et al., 2000). Receptor tyrosine-protein kinase HER2, also known as erbB-2, is included in the epidermal growth factor receptor (EGFR) family of receptor tyrosine kinases (Oh and Bang, 2020). HER2 is overexpressed in 20%-25% of breast cancer patients. HER2 over-expression is known as an aggressive tumor phenotype and is associated with worse survival (Parakh et al., 2017). Lapatinib, a reversible tyrosine kinase inhibitor with specificity for both EGFR and HER2, is approved for treating HER2-positive metastatic breast cancer after disease progression with trastuzumab therapy (Gradishar, 2013;Moasser and Krop, 2015). Compared with capecitabine monotherapy, lapatinib in combination with capecitabine improved objective response rate and progression-free survival (Geyer et al., 2006). Despite the effectiveness of lapatinib in HER2-positive breast cancer, acquired resistance remains a major clinical obstacle. D'Amato et al. have pointed out multiple mechanisms of ALR in breast cancers, including activation of compensatory pathways, mutation of the HER2 kinase domain, and gene amplification (D'Amato et al., 2015). Critically, there are currently no definite biomarkers to predict patients' responses to lapatinib. > With the development of gene sequencing and bioinformatics, increasing number of genetic studies have revealed the mechanism of tumorigenesis and drug resistance. By introducing microarray data and bioinformatic analysis that have been widely applied to investigate whole expression of genes in cancer, researchers have deepened their understanding of the differentially expressed genes (DEGs) and functional enrichment analysis among the complex diseases (Zhu et al., 2017). Although there are some bioinformatic studies corresponding to resistance to anti-HER2 therapies, scarce data and different laboratory conditions make it difficult to acquire reliable results.

[10] Use of a genetically engineered mouse model as a preclinical tool for HER2 breast cancer

  • Authors: H. Creedon, L. A. Balderstone, M. Muir, Jozef Balla, L. Gómez-Cuadrado et al.
  • Year: 2016
  • Venue: Disease Models & Mechanisms
  • URL: https://www.semanticscholar.org/paper/24515bdfdb4e1ac794736671d5eb6b8d00faeb3c
  • DOI: 10.1242/dmm.023143
  • PMID: 26721874
  • PMCID: 4770148
  • Citations: 12
  • Summary: The utility of a transgenic mouse model of HER2-driven breast cancer (MMTV-NIC) to define mechanisms of resistance to a pan-HER family inhibitor AZD8931 and identifies a link with EMT is demonstrated.
  • Evidence snippets:
  • Snippet 1 (score: 0.480) > Human epidermal growth factor receptor 2 (HER2) gene amplification and/or protein overexpression occurs in around 20% of breast cancers and is associated with poor prognosis. Several drugs capable of specifically targeting the HER2 pathway have been developed for use in both early and late HER2-positive disease and have had a significant impact on the treatment of HER2-positive breast cancer ; these include antibodies directed against HER2, such as trastuzumab and pertuzumab, and small molecule tyrosine kinase inhibitors that target the kinase activity of HER2 and HER1, such as lapatinib. Although initial response rates to the current HER2-targeted therapies are good, resistance is inevitable. Further tyrosine kinase inhibitors, including AZD8931 (sapatinib) and neratinib, have been developed in an attempt to improve efficacy rates and the duration of response. Preclinical studies have identified numerous mechanisms of both de novo and acquired resistance (Creedon et al., 2014;Rexer and Arteaga, 2012), although their clinical validation has been more difficult, which reflects the inability of the conventional cell-based approaches to model the complexity of the human disease adequately. > The limitation of conventional cell culture and mouse xenograft studies is well recognized as an obstacle to the effective translation of preclinical findings into clinical benefit (Sharpless and Depinho, 2006). Use of genetically engineered models in which tumours develop in situ in the context of an intact microenvironment is a viable alternative for preclinical assessment of both drug response and mechanisms of resistance (van Miltenburg and Jonkers, 2012). Generation of autochthonous tumours driven by cell-specific expression of oncogenic drivers or loss of tumour suppressors relevant to human tumours gives rise to tumours in which the histopathology and disease progression also recapitulate many aspects of the human disease, providing more relevant models with which to study drug response. > Here, we describe the use of a HER2-driven model of mammary tumorigenesis as a preclinical tool to study response and resistance mechanisms in HER2-positive breast cancer. We have used the MMTV-NIC (Neu-

[11] CMTM6 overexpression confers trastuzumab resistance in HER2-positive breast cancer

  • Authors: F. Xing, Hongli Gao, Guanglei Chen, Lisha Sun, Jiayi Sun et al.
  • Year: 2023
  • Venue: Molecular Cancer
  • URL: https://www.semanticscholar.org/paper/45639c735cdb62b0c3cbeaf290334def38df7947
  • DOI: 10.1186/s12943-023-01716-y
  • PMID: 36627608
  • PMCID: 9830830
  • Citations: 42
  • Summary: Findings highlight that CMTM6 stabilizes HER2 protein, contributing to trastuzumab resistance and implicate CMTLF-like MARVEL transmembrane domain-containing 6 as a potential prognostic marker and therapeutic target for overcomingtrastuzuab resistance in HER2+ breast cancer.
  • Evidence snippets:
  • Snippet 1 (score: 0.480) > Globally, breast cancer (BC) has replaced lung cancer as the most commonly diagnosed cancer in women, with an estimated 2.26 million new cases in 2020 [1]. BC is the leading cause of cancer-related mortality in females [2]. Disease progression after therapy and metastatic disease are the underlying causes of death in the majority of patients. > BC originates in epithelial cells of the mammary glands. Based on gene expression profiling and molecular pathology, BC can be classified into four subtypes: luminal A, luminal B, human epidermal growth factor receptor 2 (HER2+), and basal-like tumors. HER2+ BC accounts for 15-20% of all BC cases [3]. HER2+ BC is biologically and clinically aggressive, resistant to chemotherapy and hormone therapy, and associated with disease relapse, metastasis, and poor prognosis [4]. There is a urgent need for understanding the mechanisms underlying HER2-driven aggressiveness and drug resistance in BC to inform the development of more efficacious treatment regimens. > HER2 is a transmembrane tyrosine kinase receptor that belongs to the human epidermal growth factor (EGF) receptor family [5]. HER2 can be activated in a liganddependent or independent manner. HER2 overexpression serves as an oncogenic driver in the progression of BC, promoting constitutive activation of downstream signaling cascades that induce cell proliferation through the Ras-mitogen-activated protein kinase (MAPK) pathway, or inhibit cell death through the phosphatidylinositol 3′-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway [6,7]. > Trastuzumab, a humanized HER2-specific antibody drug, has changed the treatment paradigm for patients with HER2+ BC. Trastuzumab was approved in 1998 as the first anti-HER2 target therapy in metastatic HER2+ invasive BC [8]. Trastuzumab is currently used for adults with node-negative or node-positive HER2+ BC alone or in combination with anthracycline-or taxane-based chemotherapy [9].

[12] Prevalence and Outcomes of HER2-Low Versus HER2-0 Status in Patients with Metastatic Breast Cancer

  • Authors: Akshara Singareeka Raghavendra, Diane D Liu, S. Damodaran, S. Pasyar, Yu Shen et al.
  • Year: 2026
  • Venue: Cancers
  • URL: https://www.semanticscholar.org/paper/e8f237fcf852db5e15dc4c5470aacca8e0549b2e
  • DOI: 10.3390/cancers18020253
  • PMID: 41595172
  • PMCID: 12838560
  • Summary: It is found that HER2-low disease was common in both de novo and recurrent metastatic settings and was associated with longer overall survival compared with HER2-0 disease, supporting routine reassessment of HER2 status in metastatic breast cancer prior to changing therapy when feasible and underscore the need for more accurate and reproducible methods to measure low levels of HER2 expression.
  • Evidence snippets:
  • Snippet 1 (score: 0.479) > Since the US Food and Drug Administration (FDA) granted approval for T-DXd in patients with HR+/HER2-ultralow metastatic breast cancer on 27 January 2025, the distinction between HER2-0 and HER2ultralow has become clinically relevant. > The HER2 gene, also known as ERBB2, encodes the HER2 receptor protein, a transmembrane tyrosine kinase receptor that plays a crucial role in regulating cell growth, differentiation, and survival. Normal breast epithelial cells typically have one copy of the HER2 gene on each chromosome 17 and express HER2 protein at detectable levels [9]. When amplified or overexpressed, the HER2 gene drives oncogenic signaling that promotes proliferation, survival, and malignant transformation in breast cancer [10]. Historically, HER2-positive breast cancer, representing about 20% of all breast cancer cases, is characterized by high HER2 protein expression [11] and has been associated with aggressive tumor behavior and poorer clinical outcomes. > Breast cancer with low levels of HER2 protein expression below the positivity threshold represents a substantial proportion of cases, estimated to be around 40-50%, [12] and was previously categorized as HER2-negative. However, HER2-low breast cancer exhibits unique molecular characteristics that distinguish it from both HER2-positive and HER2negative subtypes. Gene expression profiling studies [13,14] have revealed differences in the genomic aberrations like copy number alterations and transcriptomic profiles of HER2-low breast tumors, indicating distinct signaling pathways; however, some studies [15,16] have shown no genomic difference between HER2-0 and HER2-low tumors. This heterogeneity suggests that distinct mechanisms may drive the growth and progression of HER2-low breast cancer, requiring tailored treatment strategies. > The main goals of this study were to measure the prevalence of HER2-low status (IHC 1+ or IHC 2+ and fluorescence in situ hybridization [FISH] negative) in a large cohort of patients with MBC, identify clinicopathological/treatment associations, and compare overall survival (OS) between patients with HER2-0 (IHC 0) and HER2-low MBC.

[13] The Biological Roles and Clinical Applications of the PI3K/AKT Pathway in Targeted Therapy Resistance in HER2-Positive Breast Cancer: A Comprehensive Review

  • Authors: Hanyi Zhong, Ziling Zhou, Han Wang, Ruo Wang, K. Shen et al.
  • Year: 2024
  • Venue: International Journal of Molecular Sciences
  • URL: https://www.semanticscholar.org/paper/084bdeb907da87efa38b570773bb1a7aabe7ba30
  • DOI: 10.3390/ijms252413376
  • PMID: 39769140
  • PMCID: 11677710
  • Citations: 33
  • Influential citations: 1
  • Summary: Current knowledge on the alteration and biological roles of the PI3K/AKT pathway, as well as its clinical applications and perspectives are summarized, providing new insights for advancing targeted therapies in HER2+ BC.
  • Evidence snippets:
  • Snippet 1 (score: 0.474) > Epidermal growth factor receptor 2-positive breast cancer (HER2+ BC) is a highly invasive and malignant type of tumor. Due to its resistance to HER2-targeted therapy, HER2+ BC has a poor prognosis and a tendency for metastasis. Understanding the mechanisms underlying this resistance and developing effective treatments for HER2+ BC are major research challenges. The phosphatidylinositol-3-kinase/protein kinase B (PI3K/AKT) pathway, which is frequently altered in cancers, plays a critical role in cellular proliferation and drug resistance. This signaling pathway activates various downstream pathways and exhibits complex interactions with other signaling networks. Given the significance of the PI3K/AKT pathway in HER2+ BC, several targeted drugs are currently in development. Multiple drugs have entered clinical trials or gained market approval, bringing new hope for HER2+ BC therapy. However, new drugs and therapies raise concerns related to safety, regulation, and ethics. Populations of different races and disease statuses exhibit varying responses to treatments. Therefore, in this review, we summarize current knowledge on the alteration and biological roles of the PI3K/AKT pathway, as well as its clinical applications and perspectives, providing new insights for advancing targeted therapies in HER2+ BC.

[14] New developments in the treatment of HER2-positive breast cancer.

  • Authors: R. Nahta
  • Year: 2012
  • Venue: Breast cancer
  • URL: https://www.semanticscholar.org/paper/b85b07bb525a22e6926e3f9730c7265c827548fd
  • DOI: 10.2147/BCTT.S24976
  • PMID: 23869176
  • Citations: 18
  • Influential citations: 1
  • Summary: The development and implementation of gene- and protein-based assays that measure potential molecular predictors of trastuzumab resistance will allow individualization of HER2-targeted therapeutic approaches, and may ultimately improve treatment of Her2-positive breast cancer.
  • Evidence snippets:
  • Snippet 1 (score: 0.473) > Multiple molecular mechanisms have been proposed to contribute to trastuzumab resistance (Figure 2). At the receptor level, mutations in the HER2 kinase domain have been associated with reduced response to trastuzumab in nonsmall cell lung cancer, 52,53 but this has not been reported in breast cancer. In addition, cell culture studies suggested that resistance is not due to changes in HER2 gene amplification, nor to reduced expression of the HER2 protein on the cell surface. 54 However, recent clinical studies suggest that metastatic lesions from primary HER2-positive breast cancers do not always maintain HER2 amplification. 55,56 In one study, up to one-third of patients with significant residual disease remaining after neoadjuvant trastuzumab-based therapy showed loss of HER2 amplification in association with poor survival rates. 55 Another study showed that 43 of 182 patients (24%) with HER2-positive primary tumors had HER2negative metastatic tumors. 56 Another plausible mechanism by which tumors may escape trastuzumab anticancer activity is epitope masking, meaning that the drug (trastuzumab) cannot recognize or physically interact with the antigen (HER2). Whether epitope masking is a clinically relevant mechanism remains unclear. However, preclinical studies suggest membrane proteins that interact with HER2 may impede accessibility of the epitope by trastuzumab. For example, MUC4 is a transmembrane glycoprotein that is overexpressed in some breast tumors. MUC4 interacts with and activates HER2, 57 impeding binding of trastuzumab to HER2. Exposure of cells to anti-MUC4 antibodies further reduced trastuzumab-HER2 interactions, suggesting that the mechanism of MUC4-mediated resistance is steric hindrance of the HER2-trastuzumab interaction. Partial masking of HER2 by MUC4 has been shown in a HER2-positive breast cancer cell line that has primary resistance to trastuzumab (JIMT1). 58

[15] Whether HER2-positive non-breast cancers are candidates for treatment with Ado-trastuzumab emtansine?

  • Authors: A. Moghaddas, A. Borhani
  • Year: 2016
  • Venue: Journal of Research in Pharmacy Practice
  • URL: https://www.semanticscholar.org/paper/8050a5680b6c550e4e7e8a5d9de570b35fc7dee0
  • DOI: 10.4103/2279-042X.192458
  • PMID: 27843957
  • PMCID: 5084478
  • Citations: 1
  • Summary: There is a paucity of data over the clinical evaluation of T-DM1 in human studies of non-breast cancer patients, so performing large and well-designed trials in this area is matter of interest and highly recommended.
  • Evidence snippets:
  • Snippet 1 (score: 0.471) > It has suggested that up to 20%, 9%, 30% of gastric, bladder, and uterine carcinosarcomas, respectively, overexpress HER2 and is associated with significantly worse outcomes. [23,31,34] n comparison to HER2 positive breast cancer by near 30% overexpression, [5] these quantities are large enough to be considering in treatment modalities. > By developing the new concern around trastuzumab resistance and on the other hand, documented efficacy of T-DM1 as better therapeutic option, T-DM1 is now in the spotlight. This review has discussed just some of the limited data showing the preclinical benefits of T-DM1 for treating HER2-positive non-breast cancer. All in vitro and in vivo study confirmed that T-DM1 administration led to prolonging overall survival and progression-free survival. Hence, by considering these promising results, it is time to assessed clinical responses by designing Phase I/II clinical trials. If future clinical results can demonstrate the similar results as preclinical data, then new era in the treatment of any HER2-positive non-breast cancer and survival prolongation will be created. > In March 2011, based on the results of the ToGA trial, [24] trastuzumab was intensively approved in gastric cancer. The introduction of trastuzumab made new term in gastric cancer entitled "HER2-positive gastric cancer," similar to HER2-positive breast cancer. This discovery gives us a clue that HER2-positive non-breast cancers are developing and identifying. Finding new agents for treatment of them are important future issues. > As an example, new advancing in the knowledge of urothelial carcinoma pathophysiology and underlying molecular mechanisms showed the most relevant molecular pathways that might demonstrate therapeutic potential. [34] The most important relevant overactive signaling networks are fibroblast growth factor receptor, PI3K/AKT/mTOR, and HER2. Any development in identifying the signaling networks on each cancer types leads to use of another possible effective treatment modality in the future. Furthermore, if clinical trials reach to same prominent results as we reviewed.

[16] Sequential HER2 blockade as effective therapy in chemorefractory, HER2 gene-amplified, RAS wild-type, metastatic colorectal cancer: learning from a clinical case

  • Authors: E. Martinelli, T. Troiani, V. Sforza, G. Martini, C. Cardone et al.
  • Year: 2018
  • Venue: ESMO Open
  • URL: https://www.semanticscholar.org/paper/93a1dd02fd70dc7331d320f30960a5519aa78cc9
  • DOI: 10.1136/esmoopen-2017-000299
  • PMID: 29387480
  • PMCID: 5786925
  • Citations: 30
  • Summary: The clinical case of a patient with HER2 gene amplified and RAS/BRAF wild-type mCRC who experienced a long lasting and relevant clinical efficacy from sequential anti-HER2 therapies is reported, suggesting that sequential HER2 blockade could be a potential therapeutic strategy.
  • Evidence snippets:
  • Snippet 1 (score: 0.470) > Background Constitutive activation of HER2-dependent intracellular signalling by HER2 gene amplification or by HER2 mutations has been demonstrated as a mechanism of primary and secondary cancer resistance to cetuximab or panitumumab in preclinical and clinical models of metastatic colorectal cancer (mCRC). Both HER2 Amplification for Colorectal Cancer Enhanced Stratification (HERACLES) cohort A and My Pathway clinical trials provided clinical evidence that anti-HER2 therapies could be active in these patients. Patient and methods HER2 gene amplification and HER2 protein overexpression analysis were performed in tumour tissue by fluorescence in situ hybridisation and immunohistochemistry. HER2 positivity was defined according to HERACLES CRC-specific HER2 scoring criteria. DNA analysis for multiple assessment of gene mutations or amplifications was carried out with the next-generation sequencing (NGS) Ion AmpliSeq Colon and Lung Cancer Panel and by using a more extensive targeted high-multiplex PCR-based NGS panel (OncoMine Comprehensive Assay). Results We report the clinical case of a patient with HER2 gene amplified and RAS/BRAF wild-type mCRC who experienced a long lasting and relevant clinical efficacy from sequential anti-HER2 therapies (trastuzumab plus lapatinib, pertuzumab plus trastuzumab, trastuzumab emtansine, trastuzumab plus capecitabine) achieving a cumulative clinical benefit of 29 months, after failure of the first three lines of standard treatments, which included all the potentially active drugs in mCRC, and which accounted for only 14 months of disease control. HER gene amplification was confirmed by NGS on two different metastatic lesions during the evolution of the disease. Conclusion The clinical case highlights the role of HER2 gene amplification as a key genetic driver of cancer development and progression in mCRC and suggests that sequential HER2 blockade could be a potential therapeutic strategy.
  • Snippet 2 (score: 0.470) > Background Constitutive activation of HER2-dependent intracellular signalling by HER2 gene amplification or by HER2 mutations has been demonstrated as a mechanism of primary and secondary cancer resistance to cetuximab or panitumumab in preclinical and clinical models of metastatic colorectal cancer (mCRC). Both HER2 Amplification for Colorectal Cancer Enhanced Stratification (HERACLES) cohort A and My Pathway clinical trials provided clinical evidence that anti-HER2 therapies could be active in these patients. Patient and methods HER2 gene amplification and HER2 protein overexpression analysis were performed in tumour tissue by fluorescence in situ hybridisation and immunohistochemistry. HER2 positivity was defined according to HERACLES CRC-specific HER2 scoring criteria. DNA analysis for multiple assessment of gene mutations or amplifications was carried out with the next-generation sequencing (NGS) Ion AmpliSeq Colon and Lung Cancer Panel and by using a more extensive targeted high-multiplex PCR-based NGS panel (OncoMine Comprehensive Assay). Results We report the clinical case of a patient with HER2 gene amplified and RAS/BRAF wild-type mCRC who experienced a long lasting and relevant clinical efficacy from sequential anti-HER2 therapies (trastuzumab plus lapatinib, pertuzumab plus trastuzumab, trastuzumab emtansine, trastuzumab plus capecitabine) achieving a cumulative clinical benefit of 29 months, after failure of the first three lines of standard treatments, which included all the potentially active drugs in mCRC, and which accounted for only 14 months of disease control. HER gene amplification was confirmed by NGS on two different metastatic lesions during the evolution of the disease. Conclusion The clinical case highlights the role of HER2 gene amplification as a key genetic driver of cancer development and progression in mCRC and suggests that sequential HER2 blockade could be a potential therapeutic strategy.

[17] Activation of PI3K/AKT/mTOR Pathway Causes Drug Resistance in Breast Cancer

  • Authors: Chao Dong, Jiao Wu, Yin Chen, J. Nie, Ceshi Chen
  • Year: 2021
  • Venue: Frontiers in Pharmacology
  • URL: https://www.semanticscholar.org/paper/1647736f4fbb0926492106e8551330e67e7734cc
  • DOI: 10.3389/fphar.2021.628690
  • PMID: 33790792
  • PMCID: 8005514
  • Citations: 312
  • Influential citations: 4
  • Summary: The critical role of the PI3K/AKT/mTOR pathway in drug resistance, the development of PI3k/AKt/m TOR inhibitors, and strategies to overcome acquired resistance to standard therapies in breast cancer are summarized.
  • Evidence snippets:
  • Snippet 1 (score: 0.469) > Breast cancer is the leading cause of cancer death in women around the world (Siegel and Miller, 2020). At the molecular level, breast cancer is a heterogeneous disease, divided into hormone/ estrogen-receptor-positive (HR+/ER+), human epidermal growth factor receptor-2-positive (HER2+) and ER/PR/HER2 triple-negative breast cancer (TNBC) with corresponding treatment strategies according to molecular subtypes (Nagini, 2017). Common treatments include endocrine therapy (ET) for HR+ disease, HER2 targeted therapy for HER2+ disease, chemotherapy, and immunotherapy for TNBC patients as well as PARP inhibitors for BRCA-mutated TNBC patients. Acquired resistance leads to tumor relapse in breast cancer, which is associated with multiple but relatively independent mechanisms, including overexpression of breast cancer resistance protein (BCRP, also called ABCG2), modification of cell cycle checkpoints, inhibition of apoptosis, and activation of multiple signaling pathways (Kartal-Yandim et al., 2016). > The PI3K/AKT/mTOR pathway has emerged as a novel target for overcoming drug resistance in recent years (Keegan et al., 2018;Verret et al., 2019). Dysregulation of this pathway is closely related to tumor progression and resistance to standard therapies in breast cancer (Guerrero-Zotano et al., 2016). The PI3K/AKT/mTOR pathway is one of the most frequently activated pathways in several types of cancers (Alzahrani, 2019). This is also one of the most important reasons for intrinsic resistance. Several drugs against the PI3K/AKT/mTOR pathway are in clinical development. In this review, we summarize the current knowledge of the PI3K/AKT/mTOR pathway related to drug resistance in breast cancer and propose an effective drug development strategy.

[18] ‘Breast Cancer Resistance Likelihood and Personalized Treatment Through Integrated Multiomics’

  • Authors: S. Mehmood, M. Faheem, Hammad Ismail, S. M. Farhat, Mahwish Ali et al.
  • Year: 2022
  • Venue: Frontiers in Molecular Biosciences
  • URL: https://www.semanticscholar.org/paper/c542ec176c594aeddb3790bb3d10767598b86ae4
  • DOI: 10.3389/fmolb.2022.783494
  • PMID: 35495618
  • PMCID: 9048735
  • Citations: 19
  • Influential citations: 1
  • Summary: This review has summarized therapeutic resistance associated with BC and the techniques used for its management, and identifies the biomarkers of disease progression and treatment progress by collective characterization and quantification of pools of biological molecules within and among the cancerous cells.
  • Evidence snippets:
  • Snippet 1 (score: 0.468) > Breast cancer is a very complex and heterogeneous disorder with unique molecular and morphological features relative to a disease which involves only a single gene or protein in a simple signaling pathway contributing toward the progression of disease in an independent and autonomous manner (Organization 2019). Various studies had represented BC heterogeneity through the differential response of the same type of BC patients to treatment and risk of developing side effects. One of the major clinical complications in the treatment of breast carcinoma patients is the development of therapeutic resistance (Luque-Bolivar et al., 2020). Recently drug resistance in BC treatment is not properly addressed, rather to focus on molecular pathways deeply; an alternative strategy of using a different drug is commonly applied. In order to reduce the adverse effects of BC treatment including drug resistance, a profound understanding of the molecular mechanism of the disease and the response to the drug is needed. Multidrug resistance (MDR) and consequent relapse on therapy are prevalent issues related to breast carcinoma as our understanding is incomplete related to the molecular mechanism of breast carcinoma disease (Waks and Winer, 2019a). Therefore, elucidating the molecular mechanisms involved in drug resistance is critical. For the management of breast cancers, the treatment decision not only depends on the Treatment with exemestane alone or in combination with an mTOR inhibitor such as everolimus (Carlini et al., 2007Chin et al., 2007Geisler et al., 2008Bahrami et al. (2020) ER+/ HER2- assessment of prognosis factors but also on the evaluation of pathological and clinical factors. Integrated data assessments of these multiple factors of breast carcinoma through multiomics can provide significant insight and hope for making therapeutic decisions (Parsons and Francavilla 2020). Major BC treatment strategies rely on the tumor subtype, immunohistochemical evaluation of prognostic elements, and seek new genetic markers to improve the diagnostic strategies and to enhance treatment outcomes with minimal side effects.

Notes

  • This provider combines search_papers_by_relevance with snippet_search.
  • No synthesis or second-stage model call is performed.
Disorder ▸

Disorder

  • Name: HER2-Positive Breast Cancer
  • Category:
  • Existing deep-research providers: falcon
  • Existing evidence reference count in YAML: 8

Key Pathophysiology Nodes

  • ERBB2 Gene Amplification
  • Constitutive Receptor Activation
  • Downstream Oncogenic Signaling
  • Uncontrolled Proliferation
  • Deep research literature mapping

Citation Inventory (for evidence mapping)

  • DOI:10.3390/biomedicines13051153
  • DOI:10.3390/cancers16152635
  • DOI:10.3390/genes15070903
  • DOI:10.3390/ijms252413376
  • DOI:10.3390/molecules30143026
Falcon ▸
Disease Pathophysiology Research Report
Edison Scientific Literature 19 citations 2026-01-24T18:49:36.142030

Disease Pathophysiology Research Report

Target Disease - Disease Name: HER2-Positive Breast Cancer - MONDO ID: MONDO:0007254 (breast carcinoma; HER2-positive is a molecularly defined subtype) - Category: Malignant neoplasm; solid tumor, breast

Pathophysiology description - Key concepts and definitions. HER2-positive breast cancer is driven by amplification/overexpression of ERBB2 (HER2), a receptor tyrosine kinase of the ErbB/EGFR family. HER2 lacks a soluble ligand and signals largely via homo- and heterodimers—particularly HER2/HER3—potently activating PI3K/AKT/mTOR and RAS/RAF/MEK/ERK pathways that regulate proliferation, survival, metabolism, and invasion (URL: https://doi.org/10.3390/genes15070903, Jul 2024). Quote: “HER2/HER3 heterodimer is highly potent in activating downstream signaling pathways, such as PI3K/AKT and MAPK.” (cheng2024acomprehensivereview pages 5-6) - Dysregulated signaling. HER2 amplification increases receptor density (often to millions of receptors/cell), enhancing ligand-independent dimerization and downstream signaling. Trastuzumab blocks HER2 ECD IV, inhibits HER2–HER3-driven PI3K signaling, and promotes ADCC, highlighting the centrality of PI3K/AKT and MAPK cascades in disease biology (URL: https://doi.org/10.3390/cancers16152635, Jul 2024) (cai2024depictingbiomarkersfor pages 2-4). Reviews consistently identify HER2 amplification/overexpression and HER2 heterodimerization as initiating events that “disrupt the balance between cell proliferation and apoptosis” through PI3K/AKT/mTOR and Ras/Raf/MEK/ERK activation (URL: https://doi.org/10.3390/ijms252413376, Dec 2024) (zhong2024thebiologicalroles pages 2-4). - Cellular processes. Hyperactive PI3K/AKT enhances survival, cell cycle progression, glucose and lipid metabolism, and EMT/invasion; RAS/MAPK promotes proliferation and transcriptional programs. PI3K/AKT also shapes an immunosuppressive microenvironment (e.g., PD-L1, TAM recruitment), contributing to metastasis and therapeutic resistance (URL: https://doi.org/10.3390/ijms252413376, Dec 2024) (zhong2024thebiologicalroles pages 2-4, zhong2024thebiologicalroles pages 14-16). - Immune mechanisms. Anti-HER2 mAbs (trastuzumab) exert Fc-mediated effects including ADCC and macrophage ADCP in addition to signaling blockade (URL: https://doi.org/10.3390/cancers16152635, Jul 2024) (cai2024depictingbiomarkersfor pages 2-4). ADCs add cytotoxic payload delivery and, depending on linker/payload, “bystander” killing of neighboring cells (URL: https://doi.org/10.3390/ijms252413376, Dec 2024) (zhong2024thebiologicalroles pages 1-2). - Clinical phenotype and CNS tropism. HER2-positive disease comprises ~15–25% of breast cancers and is clinically aggressive with a high risk of brain metastases; approximately 25–50% of patients with HER2-positive metastatic breast cancer develop brain metastases during the disease course (URL: https://doi.org/10.3390/biomedicines13051153, May 2025) (miski2025her2positivebreastcancer—current pages 1-2) (zhong2024thebiologicalroles pages 1-2, zhong2024thebiologicalroles pages 2-4).

1) Core Pathophysiology - Primary pathophysiological mechanisms. HER2 gene amplification/overexpression drives constitutive HER2 signaling, particularly via HER2/HER3 heterodimers, activating PI3K/AKT/mTOR and RAS/RAF/MEK/ERK pathways that promote proliferation, survival, and invasion (URL: https://doi.org/10.3390/genes15070903, Jul 2024; https://doi.org/10.3390/ijms252413376, Dec 2024) (cheng2024acomprehensivereview pages 5-6, zhong2024thebiologicalroles pages 2-4). - Dysregulated molecular pathways. Central: PI3K/AKT/mTOR (lipid signaling PIP2→PIP3; AKT activation via PDK1 and mTORC2), RAS/RAF/MEK/ERK (MAPK) (URL: https://doi.org/10.3390/ijms252413376, Dec 2024) (zhong2024thebiologicalroles pages 2-4). Crosstalk with ER signaling in HR+/HER2+ disease enables escape from anti-HER2 therapy (URL: https://doi.org/10.3390/ijms252413376, Dec 2024; https://doi.org/10.3390/genes15070903, Jul 2024) (zhong2024thebiologicalroles pages 14-16, cheng2024acomprehensivereview pages 5-6). - Cellular processes affected. Cell cycle progression (cyclin/CDK activation), survival and anti-apoptosis (AKT signaling), EMT and invasion (e.g., integrin/FAK/PI3K/AKT; lipid mediators), metabolic rewiring (AKT-driven glucose/lipid metabolism), and microenvironmental immune suppression (TAMs, CAFs) (URL: https://doi.org/10.3390/ijms252413376, Dec 2024) (zhong2024thebiologicalroles pages 14-16).

2) Key Molecular Players - Genes/Proteins (HGNC): ERBB2/HER2 (HGNC:3430), ERBB3/HER3 (HGNC:3431), EGFR/ERBB1 (HGNC:3236), PIK3CA (HGNC:8975), PTEN (HGNC:9588), AKT1 (HGNC:391), MAPK1 (HGNC:6871), MAPK3 (HGNC:6877), GRB7 (HGNC:4567), ESR1 (HGNC:3467). Mechanistically, trastuzumab blocks HER2 ECD IV and reduces HER3 phosphorylation and PI3K signaling; HER2/HER3 dimers are potent PI3K activators; PIK3CA mutations and PTEN loss increase PI3K output; GRB7 can maintain downstream ERK/AKT signaling and contribute to resistance (URLs: https://doi.org/10.3390/cancers16152635, Jul 2024; https://doi.org/10.3390/genes15070903, Jul 2024; https://doi.org/10.3390/ijms252413376, Dec 2024) (cai2024depictingbiomarkersfor pages 2-4, cheng2024acomprehensivereview pages 5-6, zhong2024thebiologicalroles pages 14-16). - Chemical entities (selected): anti-HER2 mAbs and ADCs (trastuzumab; ado-trastuzumab emtansine/T-DM1; trastuzumab deruxtecan/T-DXd), and TKIs (lapatinib, neratinib, tucatinib, pyrotinib) that variably penetrate the CNS and inhibit HER2/EGFR family kinases (URLs: https://doi.org/10.3390/ijms252413376, Dec 2024; https://doi.org/10.3390/cancers16152635, Jul 2024) (zhong2024thebiologicalroles pages 1-2, cai2024depictingbiomarkersfor pages 2-4). - Cell types (CL terms): breast carcinoma epithelial cells (CL:0000066-derived), tumor-associated macrophages (CL:0000235), CD8+ T cells (CL:0000625), cancer-associated fibroblasts/fibroblasts (CL:0000057). Microenvironmental TAMs and CAFs promote PI3K/AKT signaling, immunosuppression, and EMT (URL: https://doi.org/10.3390/ijms252413376, Dec 2024) (zhong2024thebiologicalroles pages 14-16). - Anatomical locations (UBERON): breast (UBERON:0000310), lymph node (UBERON:0000029), brain (UBERON:0000955), bone (UBERON:0001474), liver (UBERON:0002107), lung (UBERON:0002048). High CNS metastasis propensity in HER2+ disease is well documented (URL: https://doi.org/10.3390/biomedicines13051153, May 2025) (miski2025her2positivebreastcancer—current pages 1-2).

3) Biological Processes (GO annotation) - Signaling: transmembrane receptor protein tyrosine kinase signaling pathway (GO:0007169); phosphatidylinositol 3-kinase signaling (GO:0014065); MAPK cascade (GO:0000165/GO:0000187); regulation of ER signaling (cross-talk) (GO:0030520). Activation of PI3K/AKT and MAPK downstream of HER2/HER3 is the central driver (URLs: https://doi.org/10.3390/ijms252413376, Dec 2024; https://doi.org/10.3390/genes15070903, Jul 2024) (zhong2024thebiologicalroles pages 2-4, cheng2024acomprehensivereview pages 5-6). - Cellular programs: positive regulation of cell proliferation (GO:0008284); epithelial to mesenchymal transition (GO:0001837); regulation of cell cycle (GO:0051726); apoptotic process (GO:0006915); glucose metabolic process (GO:0006006) and lipid metabolic process (GO:0006629) via AKT; immune response/ADCC-related processes (GO:0006955). PI3K/AKT contributes to EMT and immune evasion (URL: https://doi.org/10.3390/ijms252413376, Dec 2024) (zhong2024thebiologicalroles pages 14-16). - Transport and trafficking: endocytosis and receptor internalization (GO:0006897), vesicle-mediated transport (GO:0016192), lysosomal degradation (GO:0009056 context), relevant for HER2 turnover and ADC processing (URL: https://doi.org/10.3390/genes15070903, Jul 2024) (cheng2024acomprehensivereview pages 5-6).

4) Cellular Components (GO:CC) - Plasma membrane (GO:0005886) and receptor complex at the membrane; early/late endosomes (GO:0005768/GO:0005769) and lysosome (GO:0005764) for receptor downregulation and ADC trafficking; cytosol (GO:0005829) and nucleus (GO:0005634) for downstream signaling transcriptional responses; extracellular region (GO:0005576) for ADC bystander payload diffusion (URLs: https://doi.org/10.3390/genes15070903, Jul 2024; https://doi.org/10.3390/ijms252413376, Dec 2024) (cheng2024acomprehensivereview pages 5-6, zhong2024thebiologicalroles pages 1-2).

5) Disease Progression - Sequence of events. (i) ERBB2 amplification → HER2 overexpression (40–100×; up to ~2 million receptors/cell) enables ligand-independent dimerization (notably with HER3); (ii) acute activation of PI3K/AKT/mTOR and MAPK cascades drives proliferation/survival; (iii) microenvironmental conditioning (TAM/CAF-driven immunosuppression, EMT) promotes invasion and dissemination; (iv) clinical metastasis with high CNS risk, reflecting both tumor-intrinsic biology and limited BBB penetration of large antibodies; (v) therapy-induced selective pressures yield resistance via PI3K/AKT reactivation (PIK3CA, PTEN), HER family rewiring (HER3 upregulation), ER crosstalk, and ADC- or TKI-specific mechanisms (URLs: https://doi.org/10.3390/cancers16152635, Jul 2024; https://doi.org/10.3390/ijms252413376, Dec 2024; https://doi.org/10.3390/biomedicines13051153, May 2025) (cai2024depictingbiomarkersfor pages 2-4, zhong2024thebiologicalroles pages 2-4, miski2025her2positivebreastcancer—current pages 1-2). - Stages/phases. Early localized disease (HER2-driven proliferation), regional spread (lymph nodes), distant metastasis with tropism for brain/liver/lung/bone; brain metastases are frequent (25–50%) and a major cause of mortality (URL: https://doi.org/10.3390/biomedicines13051153, May 2025) (miski2025her2positivebreastcancer—current pages 1-2).

6) Phenotypic Manifestations (HP terms) - Breast carcinoma (HP:0100013) with aggressive clinical course (Neoplasm aggressiveness, HP:0025315), high relapse risk without targeted therapy, and frequent brain metastases (HP:0031426) and leptomeningeal disease in advanced cases (HP:0031746). Neurologic symptoms in CNS involvement include headache, seizures, and focal deficits (clinical phenotype aligns with brain metastasis biology) (URL: https://doi.org/10.3390/biomedicines13051153, May 2025) (miski2025her2positivebreastcancer—current pages 1-2).

Resistance to anti-HER2 therapies (mechanisms and recent insights) - PI3K/AKT pathway alterations. PIK3CA activating mutations and PTEN loss restore downstream signaling and drive resistance to trastuzumab, pertuzumab, TKIs, and ADCs; PI3K/AKT activation also promotes EMT and immune evasion (URL: https://doi.org/10.3390/ijms252413376, Dec 2024) (zhong2024thebiologicalroles pages 1-2, zhong2024thebiologicalroles pages 2-4, zhong2024thebiologicalroles pages 14-16). - HER family rewiring. Upregulation of HER3 and maintenance of HER2–HER3 signaling sustain PI3K activation under HER2 blockade; ECD alterations and increased HER2 expression can reduce antibody efficacy (URL: https://doi.org/10.3390/ijms252413376, Dec 2024) (zhong2024thebiologicalroles pages 2-4). - ER crosstalk (HR+/HER2+). Approximately half of HER2+ tumors express ER; bidirectional crosstalk allows ER-driven escape from anti-HER2 therapy, supporting combined endocrine plus anti-HER2 or PI3K/AKT/mTOR blockade (URLs: https://doi.org/10.3390/ijms252413376, Dec 2024; https://doi.org/10.3390/genes15070903, Jul 2024) (zhong2024thebiologicalroles pages 14-16, cheng2024acomprehensivereview pages 5-6). - ADC-specific resistance. Mechanisms include reduced target antigen/heterogeneity, impaired internalization/trafficking, lysosomal dysfunction, drug efflux, and payload-specific alterations (e.g., TOP1 mutations with DXd). Design features (cleavable linkers, DAR, hydrophilic masking) modulate bystander effects and resistance profiles (URL: https://doi.org/10.3390/molecules30143026, Jul 2025) (li2025recentresearchadvances pages 15-17). - BBB and brain metastasis biology. Large antibodies have poor BBB penetration, permitting CNS relapse even with systemic control; CNS-active TKIs (e.g., tucatinib, neratinib) and potent ADCs (e.g., T-DXd) have improved intracranial activity, changing management of HER2+ brain metastases (URL: https://doi.org/10.3390/biomedicines13051153, May 2025) (miski2025her2positivebreastcancer—current pages 1-2).

Immune mechanisms and ADC pharmacology - ADCC/ADCP. Trastuzumab engages Fcγ receptors on NK cells and macrophages, mediating ADCC/ADCP and contributing significantly to efficacy; it also reduces HER2/HER3 signaling and can increase PTEN activity via Src inhibition (URL: https://doi.org/10.3390/cancers16152635, Jul 2024) (cai2024depictingbiomarkersfor pages 2-4). - ADC bystander effect and cytotoxicity. Modern ADCs (e.g., T-DXd) use cleavable linkers and membrane-permeable payloads to produce bystander killing, enhancing efficacy in heterogeneous tumors; this property is repeatedly emphasized in recent reviews (URL: https://doi.org/10.3390/ijms252413376, Dec 2024) (zhong2024thebiologicalroles pages 1-2).

Recent developments and latest research (2023–2024 priority) - Centrality of PI3K/AKT in resistance and therapeutic combinations. 2024 reviews summarize how PI3K/AKT alterations, microenvironmental crosstalk, and ER signaling sustain resistance, motivating rational combinations (e.g., anti-HER2 + endocrine ± PI3K/AKT/mTOR inhibitors) (URL: https://doi.org/10.3390/ijms252413376, Dec 2024) (zhong2024thebiologicalroles pages 1-2, zhong2024thebiologicalroles pages 14-16). - Updated mechanistic reviews of HER2 biology. 2024 synthesis details HER2 regulation, HER2/HER3 potency, and post-translational control (e.g., ubiquitination, HSP90) relevant to receptor turnover and drug sensitivity (URL: https://doi.org/10.3390/genes15070903, Jul 2024) (cheng2024acomprehensivereview pages 5-6). - Biomarkers of resistance. 2024 review catalogs predictive biomarkers for resistance across mAbs, TKIs, and ADCs, including PIK3CA/PTEN, HER family rewiring, and immune contexture, with treatment implications (URL: https://doi.org/10.3390/cancers16152635, Jul 2024) (cai2024depictingbiomarkersfor pages 1-2, cai2024depictingbiomarkersfor pages 2-4).

Current applications and real-world implementations - Standard-of-care anti-HER2 backbones (trastuzumab + pertuzumab + taxane) and use of TKIs and ADCs in advanced settings remain central, with evolving adoption of CNS-active regimens for brain metastases (neratinib, tucatinib, T-DM1, T-DXd) (URL: https://doi.org/10.3390/biomedicines13051153, May 2025) (miski2025her2positivebreastcancer—current pages 1-2).

Expert opinions and analysis - Reviews converge on: (i) HER2/HER3-driven PI3K/AKT as the dominant oncogenic axis; (ii) resistance via PI3K/AKT reactivation, HER3 upregulation, ER crosstalk, and ADC/TKI-specific mechanisms; (iii) need for rational combinations and CNS-active strategies due to BBB constraints and high BrM incidence (URLs: https://doi.org/10.3390/ijms252413376, Dec 2024; https://doi.org/10.3390/cancers16152635, Jul 2024; https://doi.org/10.3390/genes15070903, Jul 2024) (zhong2024thebiologicalroles pages 1-2, zhong2024thebiologicalroles pages 2-4, cai2024depictingbiomarkersfor pages 1-2, zhong2024thebiologicalroles pages 14-16, cheng2024acomprehensivereview pages 5-6, cai2024depictingbiomarkersfor pages 2-4).

Relevant statistics and data - Incidence: HER2-positive constitutes ~15–25% of breast cancers (2024 reviews) (URLs: https://doi.org/10.3390/ijms252413376, Dec 2024; https://doi.org/10.3390/cancers16152635, Jul 2024) (zhong2024thebiologicalroles pages 1-2, cai2024depictingbiomarkersfor pages 1-2). - Receptor abundance: HER2 amplification can yield ~25–50 copies of ERBB2 and ~40–100-fold increase in receptor number (≈2 million receptors/cell) (URL: https://doi.org/10.3390/cancers16152635, Jul 2024) (cai2024depictingbiomarkersfor pages 2-4). - CNS risk: 25–50% of HER2-positive metastatic breast cancer patients develop brain metastases, a leading contributor to mortality (URL: https://doi.org/10.3390/biomedicines13051153, May 2025) (miski2025her2positivebreastcancer—current pages 1-2).

Ontology-linked annotations - Genes/Proteins (HGNC): ERBB2 (HGNC:3430), ERBB3 (HGNC:3431), PIK3CA (HGNC:8975), PTEN (HGNC:9588), AKT1 (HGNC:391), MAPK1 (HGNC:6871), MAPK3 (HGNC:6877), ESR1 (HGNC:3467), GRB7 (HGNC:4567). Evidence: signaling and resistance roles as above (zhong2024thebiologicalroles pages 1-2, zhong2024thebiologicalroles pages 2-4, zhong2024thebiologicalroles pages 14-16, cheng2024acomprehensivereview pages 5-6, cai2024depictingbiomarkersfor pages 2-4). - Biological Processes (GO): GO:0007169; GO:0014065; GO:0000165/GO:0000187; GO:0008284; GO:0001837; GO:0006915; GO:0006006; GO:0006629; GO:0006955; GO:0016192 (zhong2024thebiologicalroles pages 2-4, zhong2024thebiologicalroles pages 14-16, cheng2024acomprehensivereview pages 5-6). - Cellular Components (GO:CC): GO:0005886; GO:0005768/GO:0005769; GO:0005764; GO:0005829; GO:0005634; GO:0005576 (cheng2024acomprehensivereview pages 5-6, zhong2024thebiologicalroles pages 1-2). - Phenotype associations (HP): HP:0100013; HP:0025315; HP:0031426; HP:0031746 (miski2025her2positivebreastcancer—current pages 1-2). - Cell types (CL): CL:0000066; CL:0000235; CL:0000625; CL:0000057 (zhong2024thebiologicalroles pages 14-16). - Anatomical locations (UBERON): UBERON:0000310; UBERON:0000029; UBERON:0000955; UBERON:0001474; UBERON:0002107; UBERON:0002048 (miski2025her2positivebreastcancer—current pages 1-2). - Chemical entities (CHEBI; selected metabolites central to signaling): PIP2 (CHEBI:18348), PIP3 (CHEBI:16618). Therapeutics are referenced by name due to inconsistent CHEBI coverage for biologics/ADCs (zhong2024thebiologicalroles pages 2-4).

Direct supporting quotations - “HER2/HER3 heterodimer is highly potent in activating downstream signaling pathways, such as PI3K/AKT and MAPK.” (URL: https://doi.org/10.3390/genes15070903, Jul 2024) (cheng2024acomprehensivereview pages 5-6) - “HER2-targeted therapies work by preventing receptor dimerization … and by inhibiting kinase activity … The PI3K/AKT pathway is frequently altered … and plays a central role in proliferation and drug resistance.” (URL: https://doi.org/10.3390/ijms252413376, Dec 2024) (zhong2024thebiologicalroles pages 1-2) - “Trastuzumab … binds HER2 ECD IV … and [induces] ADCC … [and] inhibits PI3K/AKT signaling … by promoting PTEN activity (via Src inhibition).” (URL: https://doi.org/10.3390/cancers16152635, Jul 2024) (cai2024depictingbiomarkersfor pages 2-4) - “Approximately 25–50% of patients with HER2-positive breast cancer experience brain metastases.” (URL: https://doi.org/10.3390/biomedicines13051153, May 2025) (miski2025her2positivebreastcancer—current pages 1-2)

Evidence items with URLs and dates - Zhong et al., 2024, Int J Mol Sci (Dec 2024). PI3K/AKT centrality in resistance; mechanisms and combinations. URL: https://doi.org/10.3390/ijms252413376 (zhong2024thebiologicalroles pages 1-2, zhong2024thebiologicalroles pages 2-4, zhong2024thebiologicalroles pages 14-16) - Cheng, 2024, Genes (Jul 2024). HER2 biology and HER2/HER3 potency and regulation. URL: https://doi.org/10.3390/genes15070903 (cheng2024acomprehensivereview pages 5-6) - Cai et al., 2024, Cancers (Jul 2024). Biomarkers of resistance; clinical agents; mechanistic roles for ADCC/PI3K. URL: https://doi.org/10.3390/cancers16152635 (cai2024depictingbiomarkersfor pages 1-2, cai2024depictingbiomarkersfor pages 2-4) - Miski et al., 2025, Biomedicines (May 2025). CNS tropism; 25–50% BrM; therapeutic landscape including CNS-active agents. URL: https://doi.org/10.3390/biomedicines13051153 (miski2025her2positivebreastcancer—current pages 1-2) - Li et al., 2025, Molecules (Jul 2025). ADC design features and resistance modes; TOP1 payload context. URL: https://doi.org/10.3390/molecules30143026 (li2025recentresearchadvances pages 15-17)

Notes on scope and limitations - Where possible, we prioritized 2023–2024 sources; several 2024 reviews directly address HER2 signaling and resistance. Some quantitative epidemiology (CNS risk) is from a 2025 synthesis but aligns with longstanding observations. Mechanistic details are consistent across multiple 2024 reviews. Future work can add primary PMIDs for individual molecular events (e.g., specific PIK3CA/PTEN mutations and clinical correlations) and incorporate guideline updates for HER2-low as new evidence is fully appraised.

References

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