One in eight American women will have breast cancer during the course of her lifetime. For most of these women, the cause is not known. Only 5-10% of all breast cancers are related to the presence of a certain inherited mutations in the BRCA1 or BRCA2 (BRCA1/2) genes. Between 20-25% of breast cancers appear in women with strong family history of breast cancer—and no identified BRCA1/2 mutation.