Breast and ovarian cancers are common cancers that affect women. But only some of them are hereditary. Hereditary cancer can happen when a parent passes on a mutation (change) in a BRCA1 or BRCA2 gene to a son or daughter. Changes in these 2 genes cause about 3% to 5% of all cancers in the breast and up to 15% of all cancers in the ovary. Changes in the 2 genes also increase the risk for breast and/or prostate cancer in men.