breast cancer

breast cancer, familial A form of breast cancer that tends to occur in members of the same family. A number of factors have been identified as increasing the risk of breast cancer. One of the strongest is a family history of breast cancer in a relative. About 15 to 20 percent of women with breast cancer have such a family history of the disease, clearly reflecting the participation of inherited (genetic) components in the development of some breast cancers. Dominant breast cancer susceptibility genes, including BRCA1 and BRCA2, appear to be responsible for about 5 percent of all breast cancer. See also BRCA1; BRCA2; breast cancer susceptibility gene.