BRCA2 and breast cancer: Many studies, including two meta-analyses, showed that prophylactic bilateral mastectomy reduces the risk for breast cancer in unaffected women with BRCA1 [relative risk (RR)= 0.134, 95% CI, 0.019–0.937] and BRCA2 (RR= 0.183, 95% CI, 0.072–0.468) (54, 57).