Background
Retrospective cohort. N=354 breast cancer patients undergoing BRCA1/2 genetic testing (insurance-covered in Japan since 2020). Assessment of BRCA mutation prevalence and testing implementation patterns, July 2018-September 2024.
Interventions and follow up
Design: Retrospective cohort of 354 Japanese breast cancer patients undergoing insurance-covered BRCA1/2 genetic testing (since 2020) to assess pathogenic variant prevalence and detection rates
Primary endpoint: Pathogenic BRCA1/2 variant prevalence and detection rates across testing modalities
mFollow up: Through September 2024
Primary endpoint: Pathogenic BRCA1/2 variant prevalence and detection rates across testing modalities
mFollow up: Through September 2024
Results
Overall pathogenic variant rate: 12.1% (43/354); BRCA1 n=21, BRCA2 n=22
By cohort: newly diagnosed 10.1%, postoperative follow-up 20.0%, companion diagnostic 12.5%
Key finding: postoperative follow-up group had higher positivity (20.0% vs 10.1%), indicating underutilization of testing in newly diagnosed eligible patients
By cohort: newly diagnosed 10.1%, postoperative follow-up 20.0%, companion diagnostic 12.5%
Key finding: postoperative follow-up group had higher positivity (20.0% vs 10.1%), indicating underutilization of testing in newly diagnosed eligible patients
Adverse events
Main adverse events: Not applicable — genetic testing study without direct treatment exposure
Procedure-related: none reported for the testing pathway (blood draw, counseling)
Not enumerated: psychosocial and downstream surveillance/risk-reducing surgery considerations
Procedure-related: none reported for the testing pathway (blood draw, counseling)
Not enumerated: psychosocial and downstream surveillance/risk-reducing surgery considerations
Conclusions
BRCA testing identifies hereditary cancer risk in 12.1% of breast cancer patients; higher rates (20%) in postoperative follow-up suggest systematic underestimation at initial diagnosis. Proactive provider recommendation and patient education are essential to optimize hereditary risk management.
Key Limitations
Retrospective, single-region (Japan) cohort; testing-uptake selection bias; no clinical outcomes (treatment, survival) reported; cross-sectional prevalence estimate not generalizable to non-Japanese populations; companion-diagnostic and follow-up subgroups not balanced.
Clinical Context
BRCA1/2 testing in breast cancer informs targeted therapy (PARP inhibitors) and hereditary risk management for patients and relatives. Per ASCO/ESMO practice, germline testing is recommended for eligible breast cancer patients; these data highlight implementation gaps where eligible newly diagnosed patients are under-tested despite insurance coverage.