PIK3CA-mutant breast cancer is a molecularly-defined subset of breast cancer characterized by activating mutations in the PIK3CA gene, which encodes the p110α catalytic subunit of phosphatidylinositol 3-kinase (PI3K). PIK3CA mutations occur in approximately 40% of ER-positive breast cancers and 10-20% of other subtypes, making it one of the most frequently mutated oncogenes in breast cancer. Hotspot mutations (E545K, H1047R) constitutively activate the PI3K-AKT-mTOR signaling pathway. FDA approval of the PI3K inhibitor alpelisib established PIK3CA mutation as a predictive biomarker for targeted therapy.
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name: PIK3CA-Mutant Breast Cancer
creation_date: '2026-01-26T02:55:13Z'
updated_date: '2026-04-26T22:38:07Z'
description: >-
PIK3CA-mutant breast cancer is a molecularly-defined subset of breast cancer
characterized by activating mutations in the PIK3CA gene, which encodes the
p110α catalytic subunit of phosphatidylinositol 3-kinase (PI3K). PIK3CA
mutations occur in approximately 40% of ER-positive breast cancers and 10-20%
of other subtypes, making it one of the most frequently mutated oncogenes in
breast cancer. Hotspot mutations (E545K, H1047R) constitutively activate the
PI3K-AKT-mTOR signaling pathway. FDA approval of the PI3K inhibitor alpelisib
established PIK3CA mutation as a predictive biomarker for targeted therapy.
categories:
- Molecularly-Defined Cancer
- Breast Cancer Subtype
- Solid Tumor
parents:
- breast carcinoma
pathophysiology:
- name: PIK3CA Oncogenic Mutations
description: >-
Activating PIK3CA mutations occur as somatic events in breast cancer cells.
Hotspot mutations cluster in the helical domain (E542K, E545K) and kinase
domain (H1047R). These mutations cause constitutive PI3K activity independent
of upstream receptor tyrosine kinase signaling.
evidence:
- reference: DOI:10.1158/2159-8290.cd-23-0944
reference_title: "Discovery and Clinical Proof-of-Concept of RLY-2608, a First-in-Class Mutant-Selective Allosteric PI3Kα Inhibitor That Decouples Antitumor Activity from Hyperinsulinemia"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: PIK3CA (PI3Kα) is a lipid kinase commonly mutated in cancer, including ∼40% of hormone receptor–positive breast cancer. The most frequently observed mutants occur in the kinase and helical domains.
explanation: Establishes hotspot helical and kinase domain PIK3CA mutations as the recurrent activating lesions in HR+ 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: phosphatidylinositol 3-kinase signaling
modifier: INCREASED
term:
id: GO:0043491
label: phosphatidylinositol 3-kinase/protein kinase B signal transduction
downstream:
- target: Constitutive PI3K-AKT Pathway Activation
description: Mutant p110α drives pathway signaling
- name: Constitutive PI3K-AKT Pathway Activation
description: >-
Mutant PI3K generates phosphatidylinositol (3,4,5)-trisphosphate (PIP3),
recruiting and activating AKT (protein kinase B). Activated AKT phosphorylates
numerous substrates promoting cell survival, proliferation, metabolism,
and resistance to apoptosis.
evidence:
- reference: DOI:10.1038/s41416-024-02852-y
reference_title: "Functional activation of the AKT-mTOR signalling axis in a real-world metastatic breast cancer cohort"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Oncogenic alterations of the PIK3CA/AKT/PTEN pathway were identified in 49.7% of cases.
explanation: Real-world metastatic breast cancer cohort confirms PIK3CA pathway alterations drive constitutive AKT activation in nearly half of cases.
biological_processes:
- preferred_term: phosphatidylinositol-mediated signaling
modifier: INCREASED
term:
id: GO:0048015
label: phosphatidylinositol-mediated signaling
- preferred_term: protein kinase B signaling
modifier: INCREASED
term:
id: GO:0043491
label: phosphatidylinositol 3-kinase/protein kinase B signal transduction
downstream:
- target: mTOR Pathway Activation
description: AKT activates mTORC1 signaling
- target: Cell Survival and Proliferation
description: AKT substrates promote tumor growth
- name: mTOR Pathway Activation
description: >-
AKT activates mTORC1 by inhibiting the TSC1/TSC2 complex, relieving suppression
of the small GTPase Rheb. Active mTORC1 promotes protein synthesis, cell
growth, and metabolic reprogramming through S6K1 and 4E-BP1 phosphorylation.
evidence:
- reference: DOI:10.1038/s41416-024-02852-y
reference_title: "Functional activation of the AKT-mTOR signalling axis in a real-world metastatic breast cancer cohort"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: High phosphorylation levels of the PI3K/AKT/mTOR downstream target p70S6 Kinase (T389) were associated with shorter PFS in patients treated with CDK4/6 inhibitors in combination with ET
explanation: Phosphoproteomic data show mTOR pathway readouts (p70S6K T389) are activated in PIK3CA-pathway breast cancers and predict worse outcomes.
biological_processes:
- preferred_term: TOR signaling
modifier: INCREASED
term:
id: GO:0031929
label: TOR signaling
downstream:
- target: Enhanced Protein Synthesis
description: mTOR drives cap-dependent translation
- name: Cell Survival and Proliferation
description: >-
PI3K-AKT signaling promotes cell survival through phosphorylation and
inactivation of pro-apoptotic proteins (BAD, FOXO transcription factors)
and cell proliferation through multiple mechanisms including cyclin D1
stabilization.
evidence:
- reference: DOI:10.1158/2159-8290.cd-23-0944
reference_title: "Discovery and Clinical Proof-of-Concept of RLY-2608, a First-in-Class Mutant-Selective Allosteric PI3Kα Inhibitor That Decouples Antitumor Activity from Hyperinsulinemia"
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: RLY-2608 inhibited tumor growth in PIK3CA-mutant xenograft models with minimal impact on insulin
explanation: Mutant-selective PI3Kα inhibition reduces PIK3CA-mutant tumor growth, consistent with the proliferative dependency on PI3K-AKT signaling.
biological_processes:
- preferred_term: negative regulation of apoptotic process
modifier: INCREASED
term:
id: GO:0043066
label: negative regulation of apoptotic process
- preferred_term: cell population proliferation
modifier: INCREASED
term:
id: GO:0008283
label: cell population proliferation
- name: Endocrine Resistance
description: >-
In ER+ breast cancer, PIK3CA mutations confer partial resistance to endocrine
therapy through crosstalk between PI3K and ER signaling. PI3K pathway
activation can maintain tumor growth despite estrogen deprivation.
evidence:
- reference: DOI:10.1186/s13058-023-01718-0
reference_title: "Interplay between ESR1/PIK3CA codon variants, oncogenic pathway alterations and clinical phenotype in patients with metastatic breast cancer (MBC): comprehensive circulating tumor DNA (ctDNA) analysis"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: ESR1 and PIK3CA codon variants, together with alterations in specific oncogenic pathways, can differentially impact the biology and clinical phenotype of luminal-like MBC.
explanation: ctDNA analysis demonstrates ESR1/PIK3CA crosstalk shapes luminal-like metastatic breast cancer biology, supporting endocrine resistance via PI3K-ER pathway interplay.
biological_processes:
- preferred_term: intracellular estrogen receptor signaling pathway
modifier: ABNORMAL
term:
id: GO:0030520
label: estrogen receptor signaling pathway
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: SUPPORT
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: >-
PIK3CA mutations occur across breast cancer subtypes but are most frequent
in ER+ disease. Tumors are typically invasive ductal carcinomas.
phenotype_term:
preferred_term: Breast carcinoma
term:
id: HP:0003002
label: Breast carcinoma
evidence:
- reference: DOI:10.1158/2159-8290.cd-23-0944
reference_title: "Discovery and Clinical Proof-of-Concept of RLY-2608, a First-in-Class Mutant-Selective Allosteric PI3Kα Inhibitor That Decouples Antitumor Activity from Hyperinsulinemia"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: PIK3CA (PI3Kα) is a lipid kinase commonly mutated in cancer, including ∼40% of hormone receptor–positive breast cancer.
explanation: PIK3CA-mutant disease defines a major subset of HR+ breast carcinoma.
- category: Molecular
name: PIK3CA Mutation
frequency: OBLIGATE
diagnostic: true
description: >-
Defining feature is presence of activating PIK3CA mutation. Three hotspots
(E542K, E545K, H1047R) account for approximately 80% of mutations. Testing
by NGS or PCR-based assays is required for treatment selection.
phenotype_term:
preferred_term: Neoplasm
term:
id: HP:0002664
label: Neoplasm
evidence:
- reference: DOI:10.1158/2159-8290.cd-23-0944
reference_title: "Discovery and Clinical Proof-of-Concept of RLY-2608, a First-in-Class Mutant-Selective Allosteric PI3Kα Inhibitor That Decouples Antitumor Activity from Hyperinsulinemia"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The most frequently observed mutants occur in the kinase and helical domains.
explanation: The defining diagnostic feature of this entity is an activating PIK3CA mutation in a hotspot codon.
biochemical:
- name: PIK3CA Mutation Testing
notes: >-
PIK3CA mutation testing is required for alpelisib eligibility. Can be
performed on tumor tissue or circulating tumor DNA (ctDNA). FDA-approved
companion diagnostics include therascreen PIK3CA RGQ PCR Kit and
FoundationOne CDx.
evidence:
- reference: DOI:10.1186/s13058-023-01718-0
reference_title: "Interplay between ESR1/PIK3CA codon variants, oncogenic pathway alterations and clinical phenotype in patients with metastatic breast cancer (MBC): comprehensive circulating tumor DNA (ctDNA) analysis"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: a multi-institutional cohort comprising 703 patients with luminal-like MBC characterized for circulating tumor DNA through next generation sequencing (NGS).
explanation: Demonstrates ctDNA NGS as a clinically used test for PIK3CA mutations in metastatic breast cancer.
genetic:
- name: PIK3CA
association: Somatic Activating Mutations
inheritance:
- name: Somatic
evidence:
- reference: DOI:10.1158/2159-8290.cd-23-0944
reference_title: "Discovery and Clinical Proof-of-Concept of RLY-2608, a First-in-Class Mutant-Selective Allosteric PI3Kα Inhibitor That Decouples Antitumor Activity from Hyperinsulinemia"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: PIK3CA (PI3Kα) is a lipid kinase commonly mutated in cancer, including ∼40% of hormone receptor–positive breast cancer.
explanation: PIK3CA mutations in breast cancer are somatic events arising in tumor cells.
notes: >-
PIK3CA (3q26.32) encodes p110α, the catalytic subunit of class IA PI3K.
Activating mutations occur somatically. Hotspot mutations: E542K and E545K
in exon 9 (helical domain) disrupt inhibitory interaction with p85 regulatory
subunit; H1047R in exon 20 (kinase domain) enhances membrane binding and
catalytic activity. Both mechanisms result in constitutive kinase activity.
evidence:
- reference: DOI:10.1158/2159-8290.cd-23-0944
reference_title: "Discovery and Clinical Proof-of-Concept of RLY-2608, a First-in-Class Mutant-Selective Allosteric PI3Kα Inhibitor That Decouples Antitumor Activity from Hyperinsulinemia"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The most frequently observed mutants occur in the kinase and helical domains.
explanation: Confirms that PIK3CA hotspot mutations cluster in helical and kinase domains in breast cancer.
treatments:
- name: Alpelisib
description: >-
PI3K alpha-selective inhibitor FDA-approved for HR+/HER2- metastatic breast
cancer with PIK3CA mutation, in combination with fulvestrant, after progression
on endocrine therapy. SOLAR-1 trial demonstrated significant PFS benefit.
Key toxicity is hyperglycemia due to PI3K role in insulin signaling.
evidence:
- reference: PMID:37743730
reference_title: "Incidence, risk factors, and management of alpelisib-associated hyperglycemia in metastatic breast cancer."
supports: SUPPORT
snippet: The combination of fulvestrant with alpelisib, a PI3K inhibitor, improves progression-free survival in metastatic hormone receptor-positive, PIK3CA-mutant breast cancer.
explanation: This abstract supports the use of alpelisib with fulvestrant in PIK3CA-mutant breast cancer.
treatment_term:
preferred_term: targeted therapy
term:
id: NCIT:C93352
label: Targeted Therapy
therapeutic_agent:
- preferred_term: alpelisib
term:
id: CHEBI:231324
label: alpelisib
- name: Inavolisib Plus Palbociclib and Fulvestrant
description: >-
FDA-approved PI3K alpha inhibitor regimen for first-line treatment of
PIK3CA-mutated, HR+/HER2- advanced or metastatic breast cancer, combining
inavolisib with palbociclib and fulvestrant.
notes: >-
INAVO120 reported improved progression-free survival for inavolisib plus
palbociclib and fulvestrant versus placebo plus palbociclib and fulvestrant;
the NEJM reference is included in this entry, but the cached abstract is
unavailable, so the quoted evidence here documents the ClinicalTrials.gov
regimen context.
evidence:
- reference: clinicaltrials:NCT04191499
reference_title: "A Phase III, Randomized, Double-Blind, Placebo-Controlled Study Evaluating the Efficacy and Safety of Inavolisib Plus Palbociclib and Fulvestrant Versus Placebo Plus Palbociclib and Fulvestrant in Patients With PIK3CA-Mutant, Hormone Receptor-Positive, HER2-Negative, Locally Advanced or Metastatic Breast Cancer"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This study will evaluate the efficacy, safety, and pharmacokinetics of inavolisib in combination with palbociclib and fulvestrant compared with placebo plus palbociclib and fulvestrant in participants with PIK3CA-mutant, hormone receptor (HR)-positive, HER2-negative locally advanced or metastatic breast cancer
explanation: ClinicalTrials.gov record for INAVO120 confirms that the studied regimen combines inavolisib with palbociclib and fulvestrant in PIK3CA-mutant HR+/HER2- advanced or metastatic breast cancer.
treatment_term:
preferred_term: pharmacotherapy
term:
id: MAXO:0000058
label: pharmacotherapy
therapeutic_agent:
- preferred_term: inavolisib
term:
id: NCIT:C132166
label: Inavolisib
- preferred_term: palbociclib
term:
id: CHEBI:85993
label: palbociclib
- preferred_term: fulvestrant
term:
id: CHEBI:31638
label: fulvestrant
- name: Endocrine Therapy Plus CDK4/6 Inhibitors
description: >-
First-line treatment for metastatic ER+/HER2- disease typically combines
aromatase inhibitors with CDK4/6 inhibitors, regardless of PIK3CA status.
Alpelisib is used after progression on this regimen.
treatment_term:
preferred_term: targeted therapy
term:
id: NCIT:C93352
label: Targeted Therapy
- name: Capivasertib
description: >-
AKT inhibitor that has shown activity in PIK3CA-mutated, AKT1-mutated,
or PTEN-altered breast cancer. Approved in combination with fulvestrant
for HR+/HER2- advanced breast cancer after prior endocrine therapy.
treatment_term:
preferred_term: pharmacotherapy
term:
id: MAXO:0000058
label: pharmacotherapy
therapeutic_agent:
- preferred_term: capivasertib
term:
id: CHEBI:229222
label: capivasertib
evidence:
- reference: DOI:10.33590/emjoncol/njqz9723
reference_title: "Second-Line Strategies to Overcome Resistance to Oestrogen Therapy in Patients with ER+/HER2- Metastatic Breast Cancer: A Year in Review"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: CAPItello-291 demonstrated a 5.5-month median PFS with capivasertib plus fulvestrant in PIK3CA/AKT1/PTEN-altered mBC in patients previously treated with CDK4/6i.
explanation: Directly supports capivasertib plus fulvestrant as a treatment option for PIK3CA/AKT1/PTEN-altered metastatic breast cancer after prior CDK4/6 inhibitor therapy.
disease_term:
preferred_term: breast carcinoma
term:
id: MONDO:0004989
label: breast carcinoma
classifications:
icdo_morphology:
classification_value: Adenocarcinoma
harrisons_chapter:
- classification_value: cancer
- classification_value: solid tumor
references:
- reference: DOI:10.1038/s41416-024-02852-y
title: Functional activation of the AKT-mTOR signalling axis in a real-world metastatic breast cancer cohort
findings: []
- reference: DOI:10.1056/nejmoa2404625
title: Inavolisib-Based Therapy in <i>PIK3CA</i> -Mutated Advanced Breast Cancer
findings: []
- reference: clinicaltrials:NCT04191499
title: A Phase III, Randomized, Double-Blind, Placebo-Controlled Study Evaluating the Efficacy and Safety of Inavolisib Plus Palbociclib and Fulvestrant Versus Placebo Plus Palbociclib and Fulvestrant in Patients With PIK3CA-Mutant, Hormone Receptor-Positive, HER2-Negative, Locally Advanced or Metastatic Breast Cancer
findings: []
- reference: DOI:10.33590/emjoncol/njqz9723
title: 'Second-Line Strategies to Overcome Resistance to Oestrogen Therapy in Patients with ER+/HER2- Metastatic Breast Cancer: A Year in Review'
findings: []
- reference: DOI:10.1101/2025.06.18.25329632
title: Clinicogenomic landscape and function of <i>PIK3CA</i> , <i>AKT1</i> , and <i>PTEN</i> mutations in breast cancer
findings: []
- reference: DOI:10.1158/2159-8290.cd-23-0944
title: Discovery and Clinical Proof-of-Concept of RLY-2608, a First-in-Class Mutant-Selective Allosteric PI3Kα Inhibitor That Decouples Antitumor Activity from Hyperinsulinemia
findings: []
- reference: DOI:10.1186/s13058-023-01718-0
title: 'Interplay between ESR1/PIK3CA codon variants, oncogenic pathway alterations and clinical phenotype in patients with metastatic breast cancer (MBC): comprehensive circulating tumor DNA (ctDNA) analysis'
findings: []
Disease Pathophysiology Research Report
Target Disease - Disease Name: PIK3CA‑Mutant Breast Cancer - MONDO ID: MONDO:0007254 (breast carcinoma; PIK3CA‑mutant subtype within HR+/HER2− predominates) - Category: Neoplasm; epithelial carcinoma
Pathophysiology description (narrative) PIK3CA encodes the p110α catalytic subunit of class IA PI3K. Oncogenic hotspot mutations cluster in the helical domain (E542K, E545K) and kinase domain (H1047R). These mutations increase conversion of PI(4,5)P2 to PIP3, leading to AKT and mTORC1/2 activation and broad transcriptional and metabolic reprogramming that supports proliferation and survival in breast cancer, especially HR+/HER2− disease where prevalence approaches ~35–40% in large series. Recent profiling across >50,000 breast tumors confirms PIK3CA as the most frequently altered PI3K‑pathway gene and details the dominance of H1047R/E545K/E542K hotspots. (tao2025clinicogenomiclandscapeand pages 1-4) Mechanistically, mutant p110α shows conformational and allosteric changes that favor the active state and enhance membrane engagement and signaling output. Orthosteric PI3Kα inhibitors suppress both mutant and wild‑type PI3Kα and cause on‑target metabolic toxicity; accordingly, mutant‑selective allosteric inhibitors (e.g., RLY‑2608) have been designed to “decouple antitumor activity from hyperinsulinemia,” with early clinical responses reported. Structural and translational work supports mutant‑selective binding pockets and allosteric control as a path to improved therapeutic index. (varkaris2024discoveryandclinical pages 1-3) Functional proteomic studies in real‑world metastatic breast cancer (MBC) cohorts demonstrate that genomic alterations incompletely predict pathway activity; many genomically wild‑type tumors exhibit AKT phosphorylation comparable to mutant tumors, and high p70S6K phosphorylation correlates with inferior PFS on CDK4/6 inhibitor plus endocrine therapy, underscoring the importance of measuring pathway activation alongside genomics. (prasad2024functionalactivationof pages 1-2)
Increased proliferation/cell‑cycle progression, survival under endocrine pressure, metabolic rewiring (glucose/insulin signaling feedback), and likely EMT/invasion in specific contexts; codon‑level variation tracks with metastatic tropism (e.g., PIK3CA 1047/542 associated with bone metastases in luminal MBC). (gerratana2023interplaybetweenesr1pik3ca pages 1-2, prasad2024functionalactivationof pages 1-2)
Key Molecular Players
Primary: Breast/mammary gland epithelium (UBERON:0001911, UBERON:0008290). Common metastatic sites for HR+ PIK3CA‑mutant disease include bone and liver; bone enrichment is noted for specific codon classes. (gerratana2023interplaybetweenesr1pik3ca pages 1-2)
Biological Processes (GO terms; disrupted)
GO:0014065 phosphatidylinositol 3‑kinase signaling; GO:0035556 intracellular signal transduction; GO:1900740 positive regulation of protein kinase B signaling; GO:0008284 positive regulation of cell proliferation; GO:0009267 cellular response to starvation; GO:0001932 regulation of protein phosphorylation; GO:0046328 regulation of JAK‑STAT/insulin signaling crosstalk (as pathway cross‑talk); GO:0001837 epithelial to mesenchymal transition (context‑specific). Evidence: pathway activation and clinical responses to PI3K/AKT targeting; phosphoprotein correlates; codon‑specific clinical phenotypes. (prasad2024functionalactivationof pages 1-2, tao2025clinicogenomiclandscapeand pages 1-4, gerratana2023interplaybetweenesr1pik3ca pages 1-2)
Cellular Components (GO CC)
Plasma membrane signaling complexes (PI3Kα at inner leaflet), cytosol (AKT), mTORC1 (lysosome) and mTORC2 (membrane‑associated), and lipid microdomains where PI(4,5)P2→PIP3 conversion occurs. Structural data highlight mutation‑specific conformations that alter membrane engagement/allosteric pockets in PI3Kα. (varkaris2024discoveryandclinical pages 1-3)
Disease Progression (sequence of events)
Clinical manifestation: Endocrine‑resistant HR+ MBC with measurable dependence on PI3K/AKT/mTOR signaling by genomics and/or phosphoproteomics. (prasad2024functionalactivationof pages 1-2)
Phenotypic Manifestations (HP terms; examples)
Recent developments and latest research (2023–2024 prioritized) - Mutant‑selective allosteric PI3Kα inhibition (RLY‑2608): First‑in‑class approach shows preclinical breadth across helical and kinase domain mutants and initial clinical responses with reduced metabolic toxicity, providing a platform for overcoming limitations of orthosteric PI3Kα inhibitors. (Cancer Discovery; DOI:10.1158/2159-8290.CD-23-0944; published Nov 2024; URL: https://doi.org/10.1158/2159-8290.cd-23-0944). (varkaris2024discoveryandclinical pages 1-3) - Functional activation vs genomics: Real‑world phosphoprotein profiling demonstrates poor concordance of mutations with pathway activity and prognostic value of p70S6K phosphorylation under CDK4/6+ET, supporting biomarker strategies that combine phospho‑signaling with genomics. (Br J Cancer; DOI:10.1038/s41416-024-02852-y; online Sep 25, 2024; URL: https://doi.org/10.1038/s41416-024-02852-y). (prasad2024functionalactivationof pages 1-2) - Codon‑level ESR1/PIK3CA interplay in luminal MBC: Large ctDNA NGS series reveals variant‑specific co‑alteration patterns and metastatic tropism (e.g., PIK3CA 1047/542 with bone metastases), emphasizing precision beyond “mutant vs wild‑type.” (Breast Cancer Research; DOI:10.1186/s13058-023-01718-0; Oct 2023; URL: https://doi.org/10.1186/s13058-023-01718-0). (gerratana2023interplaybetweenesr1pik3ca pages 1-2)
Current applications and real‑world implementations - Alpelisib (PI3Kα inhibitor) is an established therapy for HR+/HER2−, PIK3CA‑mutated MBC, but toxicity (notably hyperglycemia) limits use. Contemporary real‑world and translational analyses support that pathway activation and benefit may extend beyond strict genomic selection, advocating combined genomic and phospho‑signaling assessment in practice. (prasad2024functionalactivationof pages 1-2) - Capivasertib (AKT inhibitor) plus fulvestrant: Based on CAPItello‑291 (NEJM 2023), gained approval for HR+/HER2− advanced breast cancer with PIK3CA/AKT1/PTEN alterations; pathway‑altered subgroup doubled median PFS vs placebo+fulvestrant (7.3 vs 3.1 months) and overall cohort also benefited, providing a genomically anchored, endocrine‑based regimen post‑AI±CDK4/6i. (statistics as reported in contemporary clinicogenomic review; medRxiv 2025 summarizing NEJM 2023; URL: https://doi.org/10.1101/2025.06.18.25329632). (tao2025clinicogenomiclandscapeand pages 1-4) - Inavolisib (selective PI3Kα inhibitor with mutant p110α degradation) plus palbociclib‑fulvestrant (first‑line, INAVO120, NEJM 2024): Median PFS 15.0 vs 7.3 months (HR 0.43; P<0.001); ORR 58.4% vs 25.0%. Hyperglycemia and stomatitis increased but discontinuation remained low (6.8%). This validates intensified, mechanism‑guided triplet targeting ER/CDK4‑6/PI3Kα in PIK3CA‑mutant disease. (DOI:10.1056/NEJMoa2404625; Oct 2024; URL: https://doi.org/10.1056/nejmoa2404625). (turner2024inavolisibbasedtherapyin pages 1-2)
Expert opinions and analysis from authoritative sources - Translational and structural experts propose that mutation‑specific allosteric pockets in PI3Kα enable selective inhibition that preserves insulin signaling homeostasis, addressing a central liability of orthosteric PI3Kα inhibitors. Early clinical results with RLY‑2608 substantiate this concept. (varkaris2024discoveryandclinical pages 1-3) - Precision oncology implementation should integrate pathway phosphoprotein readouts with genomics to identify PI3K/AKT/mTOR‑driven tumors and guide sequencing with ET, CDK4/6i, PI3Kα/AKT/mTOR inhibitors post‑CDK4/6i progression. (prasad2024functionalactivationof pages 1-2)
Relevant statistics and data from recent studies - Prevalence and hotspot spectrum: In a clinicogenomic dataset of 51,767 breast tumors, PIK3CA altered in 37.4%; hotspot distribution among PIK3CA mutations: H1047R 35.6%, E545K 19.7%, E542K 11.7%. (medRxiv; Jun 18, 2025; URL: https://doi.org/10.1101/2025.06.18.25329632). (tao2025clinicogenomiclandscapeand pages 1-4) - Capivasertib+fulvestrant: Median PFS 7.3 vs 3.1 months in AKT‑pathway‑altered tumors (CAPItello‑291 summary), regulatory approval subsequently granted for HR+/HER2− ABC with PIK3CA/AKT1/PTEN alterations. (tao2025clinicogenomiclandscapeand pages 1-4, prasad2024functionalactivationof pages 1-2) - Inavolisib+palbociclib‑fulvestrant (INAVO120): Median PFS 15.0 vs 7.3 months (HR 0.43); ORR 58.4% vs 25.0%; low discontinuation despite increased grade ≥3 AEs; NEJM 2024. (turner2024inavolisibbasedtherapyin pages 1-2) - Phosphoproteomics in real‑world MBC: Genomics poorly predicted protein activation (AUC 0.69); AKT phosphorylation mirrored mutant signaling in 76.9% of genomically wild‑type tumors; high p70S6K(T389) associated with shorter PFS on CDK4/6+ET (HR 4.18). (prasad2024functionalactivationof pages 1-2) - Codon‑specific clinical patterns: PIK3CA 1047 and 542 variants associated with bone metastases in ctDNA‑profiled luminal MBC; ESR1 codon variants show distinct co‑alterations and metastatic patterns. (gerratana2023interplaybetweenesr1pik3ca pages 1-2)
Gene/protein annotations with ontology terms (examples) - PIK3CA (HGNC:8975): GO BP—phosphatidylinositol 3‑kinase signaling, positive regulation of AKT signaling; GO CC—plasma membrane, cytosol; GO MF—phosphatidylinositol 3‑kinase activity. (varkaris2024discoveryandclinical pages 1-3, prasad2024functionalactivationof pages 1-2) - AKT1 (HGNC:391): GO BP—cell proliferation, apoptosis regulation; GO CC—cytosol, plasma membrane; GO MF—protein serine/threonine kinase activity. (prasad2024functionalactivationof pages 1-2) - MTOR (HGNC:3942): GO BP—mTOR signaling, translation regulation; GO CC—lysosome (mTORC1), cytosol/membrane (mTORC2). (prasad2024functionalactivationof pages 1-2) - PTEN (HGNC:9588): GO BP—negative regulation of PI3K signaling via PIP3 dephosphorylation; GO MF—phosphatidylinositol‑3,4,5‑trisphosphate 3‑phosphatase activity. (tao2025clinicogenomiclandscapeand pages 1-4) - ESR1 (HGNC:3467): GO BP—hormone‑mediated signaling, transcription regulation; crosstalk with PI3K/AKT underlies endocrine resistance. (gerratana2023interplaybetweenesr1pik3ca pages 1-2, prasad2024functionalactivationof pages 1-2)
Phenotype associations (HP terms; examples) - Endocrine therapy resistance in HR+ MBC; metastatic bone disease; treatment‑emergent hyperglycemia with PI3Kα inhibitors. (turner2024inavolisibbasedtherapyin pages 1-2, prasad2024functionalactivationof pages 1-2)
Cell type involvement (CL terms) - Luminal mammary epithelial tumor cells (CL:0002328) as primary drivers; tumor stroma and immune cells modulate growth‑factor/insulin signaling, reinforcing PI3K pathway. (prasad2024functionalactivationof pages 1-2, gerratana2023interplaybetweenesr1pik3ca pages 1-2)
Anatomical locations (UBERON terms) - Breast/mammary gland epithelium (UBERON:0001911, UBERON:0008290); bone and liver as common sites of metastatic involvement in luminal MBC, with codon‑specific associations. (gerratana2023interplaybetweenesr1pik3ca pages 1-2)
Chemical entities (CHEBI terms; examples) - PI(4,5)P2 (CHEBI:18348), PIP3 (CHEBI:16618); pharmacologic agents: alpelisib, inavolisib, capivasertib, and experimental RLY‑2608 (mutant‑selective allosteric PI3Kα inhibitor). (prasad2024functionalactivationof pages 1-2, turner2024inavolisibbasedtherapyin pages 1-2, varkaris2024discoveryandclinical pages 1-3)
Evidence items with URLs and publication dates - Varkaris A et al. Discovery and clinical proof‑of‑concept of RLY‑2608… Cancer Discovery. Published Nov 2024. DOI:10.1158/2159-8290.CD-23-0944. URL: https://doi.org/10.1158/2159-8290.cd-23-0944 (mutant‑selective PI3Kα, structural/allosteric insights, early clinical activity). (varkaris2024discoveryandclinical pages 1-3) - Turner NC et al. Inavolisib‑Based Therapy in PIK3CA‑Mutated Advanced Breast Cancer. NEJM. Oct 2024; 391:1584‑1596. DOI:10.1056/NEJMoa2404625. URL: https://doi.org/10.1056/nejmoa2404625 (phase 3 PFS/ORR, toxicity profile). (turner2024inavolisibbasedtherapyin pages 1-2) - Prasad D et al. Functional activation of the AKT‑mTOR signalling axis… Br J Cancer. Online Sep 25, 2024. DOI:10.1038/s41416-024-02852-y. URL: https://doi.org/10.1038/s41416-024-02852-y (genomics vs phospho‑signaling, prognostic p70S6K). (prasad2024functionalactivationof pages 1-2) - Gerratana L et al. Interplay between ESR1/PIK3CA codon variants… Breast Cancer Research. Oct 2023. DOI:10.1186/s13058-023-01718-0. URL: https://doi.org/10.1186/s13058-023-01718-0 (codon‑specific co‑alterations, metastatic patterns, ctDNA utility). (gerratana2023interplaybetweenesr1pik3ca pages 1-2) - Tao JJ et al. Clinicogenomic landscape and function of PIK3CA, AKT1, and PTEN mutations in breast cancer. medRxiv. Jun 18, 2025. DOI:10.1101/2025.06.18.25329632. URL: https://doi.org/10.1101/2025.06.18.25329632 (prevalence, hotspot distribution, clinical targeting; summarizes CAPItello‑291 findings). (tao2025clinicogenomiclandscapeand pages 1-4)
Direct quotes supporting key statements - “In patients with PIK3CA‑mutated, hormone receptor‑positive, HER2‑negative locally advanced or metastatic breast cancer, inavolisib plus palbociclib‑fulvestrant led to significantly longer progression‑free survival than placebo plus palbociclib‑fulvestrant” (NEJM 2024). (turner2024inavolisibbasedtherapyin pages 1-2) - RLY‑2608 “decouples antitumor activity from hyperinsulinemia” via mutant‑selective allosteric inhibition (Cancer Discovery 2024). (varkaris2024discoveryandclinical pages 1-3) - “Genomic profiles emerged as poor predictors of protein activity (AUC: 0.69)… AKT phosphorylation levels mimicked those of mutant lesions in 76.9% of wild‑type tumours” (Br J Cancer 2024). (prasad2024functionalactivationof pages 1-2)
Clinical testing and liquid biopsy - ctDNA NGS enables codon‑level profiling of ESR1/PIK3CA and pathway co‑alterations that inform treatment selection and predict metastatic patterns; real‑world data advocate combining genomic panels with phosphoprotein markers to refine selection for PI3K/AKT‑pathway inhibitors. (gerratana2023interplaybetweenesr1pik3ca pages 1-2, prasad2024functionalactivationof pages 1-2)
Conclusions PIK3CA‑mutant breast cancer is driven by mutation‑specific activation of PI3Kα that amplifies AKT/mTOR signaling, fosters endocrine resistance, and shapes metastatic behavior. 2023–2024 data establish effective, biomarker‑guided targeting via AKT inhibition (capivasertib+fulvestrant) and next‑generation PI3Kα approaches (inavolisib triplet; mutant‑selective allosteric inhibition with RLY‑2608). Implementation should integrate genomics with phospho‑signaling to accurately identify pathway‑addicted tumors and optimize sequencing with ET and CDK4/6 inhibitors. (tao2025clinicogenomiclandscapeand pages 1-4, turner2024inavolisibbasedtherapyin pages 1-2, varkaris2024discoveryandclinical pages 1-3, prasad2024functionalactivationof pages 1-2, gerratana2023interplaybetweenesr1pik3ca pages 1-2)
References
(varkaris2024discoveryandclinical pages 1-3): Andreas Varkaris, Ermira Pazolli, Hakan Gunaydin, Qi Wang, Levi Pierce, Alessandro A. Boezio, Artemisa Bulku, Lucian DiPietro, Cary Fridrich, Adam Frost, Fabrizio Giordanetto, Erika P. Hamilton, Katherine Harris, Michael Holliday, Tamieka L. Hunter, Amanda Iskandar, Yongli Ji, Alexandre Larivée, Jonathan R. LaRochelle, André Lescarbeau, Fabien Llambi, Brenda Lormil, Mary M. Mader, Brenton G. Mar, Iain Martin, Thomas H. McLean, Klaus Michelsen, Yakov Pechersky, Erika Puente-Poushnejad, Kevin Raynor, Dipali Rogala, Ramin Samadani, Alison M. Schram, Kelley Shortsleeves, Sweta Swaminathan, Shahein Tajmir, Gege Tan, Yong Tang, Roberto Valverde, Bryan Wehrenberg, Jeremy Wilbur, Bret R. Williams, Hongtao Zeng, Hanmo Zhang, W. Patrick Walters, Beni B. Wolf, David E. Shaw, Donald A. Bergstrom, James Watters, James S. Fraser, Pascal D. Fortin, and D. Randal Kipp. Discovery and clinical proof-of-concept of rly-2608, a first-in-class mutant-selective allosteric pi3kα inhibitor that decouples antitumor activity from hyperinsulinemia. Cancer Discovery, 14:240-257, Nov 2024. URL: https://doi.org/10.1158/2159-8290.cd-23-0944, doi:10.1158/2159-8290.cd-23-0944. This article has 86 citations and is from a highest quality peer-reviewed journal.
(turner2024inavolisibbasedtherapyin pages 1-2): Nicholas C. Turner, Seock-Ah Im, Cristina Saura, Dejan Juric, Sibylle Loibl, Kevin Kalinsky, Peter Schmid, Sherene Loi, Patrapim Sunpaweravong, Antonino Musolino, Huiping Li, Qingyuan Zhang, Zbigniew Nowecki, Roland Leung, Eirini Thanopoulou, Noopur Shankar, Guiyuan Lei, Thomas J. Stout, Katherine E. Hutchinson, Jennifer L. Schutzman, Chunyan Song, and Komal L. Jhaveri. Inavolisib-based therapy in pik3ca-mutated advanced breast cancer. The New England journal of medicine, 391 17:1584-1596, Oct 2024. URL: https://doi.org/10.1056/nejmoa2404625, doi:10.1056/nejmoa2404625. This article has 215 citations and is from a highest quality peer-reviewed journal.
(prasad2024functionalactivationof pages 1-2): Deepika Prasad, Elisa Baldelli, Edik M. Blais, Justin Davis, Emna El Gazzah, Claudius Mueller, Alison Gomeiz, Aisha Ibrahim, Avani Vinayak Newrekar, Brian A. Corgiat, Rick Dunetz, Emanuel F. Petricoin III, Qi Wei, and Mariaelena Pierobon. Functional activation of the akt-mtor signalling axis in a real-world metastatic breast cancer cohort. British Journal of Cancer, 131:1543-1554, Sep 2024. URL: https://doi.org/10.1038/s41416-024-02852-y, doi:10.1038/s41416-024-02852-y. This article has 7 citations and is from a domain leading peer-reviewed journal.
(gerratana2023interplaybetweenesr1pik3ca pages 1-2): Lorenzo Gerratana, Andrew A. Davis, Marko Velimirovic, Katherine Clifton, Whitney L. Hensing, Ami N. Shah, Charles S. Dai, Carolina Reduzzi, Paolo D’Amico, Firas Wehbe, Arielle Medford, Seth A. Wander, William J. Gradishar, Amir Behdad, Fabio Puglisi, Cynthia X. Ma, Aditya Bardia, and Massimo Cristofanilli. Interplay between esr1/pik3ca codon variants, oncogenic pathway alterations and clinical phenotype in patients with metastatic breast cancer (mbc): comprehensive circulating tumor dna (ctdna) analysis. Breast Cancer Research : BCR, Oct 2023. URL: https://doi.org/10.1186/s13058-023-01718-0, doi:10.1186/s13058-023-01718-0. This article has 10 citations.
(tao2025clinicogenomiclandscapeand pages 1-4): Jacqueline J. Tao, Saumya D. Sisoudiya, Hanna Tukachinsky, Alexa Schrock, Smruthy Sivakumar, Ethan S. Sokol, and Neil Vasan. Clinicogenomic landscape and function of pik3ca, akt1, and pten mutations in breast cancer. medRxiv : the preprint server for health sciences, Jun 2025. URL: https://doi.org/10.1101/2025.06.18.25329632, doi:10.1101/2025.06.18.25329632. This article has 0 citations.