Association of tamoxifen use and reduced risk of contralateral breast cancer for BRCA1 and BRCA2 mutation carriers

Patients and methods Female BRCA1 and BRCA2 mutation carriers, with a personal history of BC since 1970, enrolled in any of the BC family studies, kConFab (Kathleen Cuningham Foundation Consortium for Research into Familial Breast Cancer), IBCCS (International BRCA1 and BRCA2 Carrier Cohort Study), or BCFR (Breast Cancer Family Registry) were eligible. Those with bilateral disease at first BC diagnosis, tamoxifen use prior to their first BC diagnosis, or another invasive cancer with were excluded. Data were self-reported at entry into the cohort and at follow-up. Hazard ratios (HRs) for development of contralateral BC associated with tamoxifen use after first BC diagnosis were estimated using Cox proportional hazards, modeling time from diagnosis of first primary BC, adjusting for year of birth (continuous), age at diagnosis (continuous), country and bilateral oophorectomy (yes/no, time-varying). Data were censored at contralateral mastectomy, death or loss to follow-up.