BRCA1 and breast cancer: Hereditary breast cancer accounts for 5%–10% of all breast cancer.4–7 The vast majority of inherited breast cancers are due to mutations in two breast cancer genes referred to as BRCA1 and 2.6 The risks of developing breast and ovarian cancer are higher in carriers of the BRCA1 mutation compared to carriers of BRCA2.8 In addition, cancer is more likely to occur at a younger age in carriers of BRCA1 mutations than in carriers of BRCA2.