Somatic mutations of BRCA1 in sporadic cancer of the breast Sounds, initially, like Knudson and RB gene redux. Many sporadic breast and ovarian cancers also show LOH at 17q markers. Assumed that BRCA1 would show somatic mutation as do other tumor suppressor genes. Surprise - all mutations in BRCA1 are constitutive for person, likely germline derived. Somatic mutations not reported yet.
Reason is unknown - reduction to handwaving about windows in development.
BRCA2 - the other breast cancer gene Linkage analyses confirmed that not all hereditary breast cancer cases were linked to chromosome 17q and BRCA1. Some, particularly those with male breast cancer, showed linkage to a 6 cM region of chromosome 13q12-q13. Ovarian cancer risk lower, male breast cancer risk markedly elevated. Other tumors may also have increased frequency. Loss of heterozygosity for chromosome 13q markers is common in diseased patients.