In the National Surgical Adjuvant Breast and Bowel Project (NSABP) Breast Cancer Prevention trial (P-1 trial), tamoxifen reduced breast cancer risk by 62% in BRCA2 P/LPV carriers (relative risk [RR] 0.38, 95% CI 0.06–1.56), but not in BRCA1 P/LPV carriers (RR 1.67, 95% CI 0.32–10.07), similar to the reduction in the incidence of ER-positive breast cancer among non-carriers in the same P-1 trial [21]. Here, BRCA1 is linked to breast cancer.