BRCA1 and breast cancer: We found that 16.8% (95% CI, 11.1%-23.9%) of participants with MpBC who underwent germline testing had PGVs in breast cancer susceptibility genes, with PGVs seen across MpBC subtypes and with most PGVs occurring in BRCA1 (11.9% variant prevalence) and BRCA2 (3.5%).