BRCA1 and breast cancer: Among women without a prior history of breast cancer, those who underwent risk-reducing BSO had a lower risk of first breast cancer diagnosis compared with those who did not: 7% versus 23% in BRCA2 carriers (HR: 0.36 (95% CI: 0.16 - 0.82)) and 14% versus 20% in BRCA1 carriers (HR: 0.63 (95% CI: 0.41 - 0.96)).