Hereditary or familial breast and ovarian cancers are responsible for approximately 5-10% of all cases of malignancy in these organs. The vast majority of breast and ovarian cancer cases are not hereditary but sporadic forms of the disease. Mutations (genetic structural changes) in genes BRCA1 or BRCA2 are currently associated with approximately 30%-70% of hereditary breast cancers and with 90% of familial ovarian cancers. Possible mutations in other genes are currently under investigation. Hereditary breast and ovarian cancer is also known as familial breast and ovarian syndrome, familial BRCA1 syndrome, or familial BRCA2 syndrome.

Families are generally suspected of bearing mutations in either BRCA1 or BRCA2 when family history shows one or more cases of breast or ovarian malignancies, affecting women of at least three or more different generations. For instance, cases of breast or ovarian tumors occurring in one grandmother or a...