BRCA1 and breast cancer: For BRCA1, relative to the before-1940 cohort, the breast cancer RRs (95% floating-CI27) were 2.5 (1.8–3.4), 2.9 (1.9–4.6) and 3.3 (1.9–5.7) for the three later birth cohorts, respectively (eTable 6).