The missense mutations in the RING domain and a protein truncating mutation in exon 11 (1806C>T), all located in BRCA1, induce comparable relative risks for breast versus ovarian cancer (3.4 and 2.1 respectively), while the BRCA2 IVS16-2G>A mutation appears to be highly predisposing for breast cancer compared to ovarian cancer. This evidence concerns the gene BRCA2 and breast cancer.