These data suggest that an association of AR CAG repeat length with increased breast cancer risk may be found only in BRCA1 or BRCA2 mutation carriers (and not individual germline without BRCA1 or BRCA2 mutations), and that AR-dependent modification of cancer risk in BRCA1 and BRCA2 mutation carriers may differ according to which gene is mutated, and the mutation position relative to AR-binding site. This evidence concerns the gene BRCA1 and cancer.