BRCA1 and breast cancer: In a meta-analysis that included 13,965 BRCA1 and 7,057 BRCA2 mutation carriers enrolled on 14 observational studies, the breast cancer risk among BRCA1 mutation carriers was lowered by RRSO (HR = 0.63, 95% CI, 0.49-0.81, P < 0.01) and BRCA2 mutation carriers (HR= 0.51, 95% CI, 0.34-0.75, P < 0.01).