Hereditary premenopausal breast cancer.

Less than 1% of breast cancers occur between the age of 20 and 30 years, but more than 50% of breast cancers under the age of 30 years are hereditary. Breast cancer mainly occurs sporadically, however, in 5 to maximally 10% of cases a genetic predisposition is present. Mutations in the already sequenced tumor suppressor genes BRCA1 and BRCA2 account for 60-70% of these hereditary breast cancers. The chromosomal location of BRCA1 is 17q21 and that of BRCA2 is 13q12-13. Screening procedures and possible prevention strategies for women with mutations in the BRCA1 and BRCA2 genes are discussed. They include the use of tamoxifen.