BRCA1 and breast cancer: Mutations in BRCA1/2 genes have an estimated lifetime risk of breast cancer between 60 and 85%, and a lifetime risk of ovarian cancer between 26 and 54% for BRCA1 and between 10 and 23% for BRCA2. They are responsible for about 45% of families with multiple cases of breast cancer and up to 90% of families with both breast and ovarian cancer [1–4].