Regarding genetic factors, high-penetrance cancer-susceptibility genes such as BRCA1 and BRCA2 are associated with some cases of familial breast cancer, though this association accounts for only about 5% of all breast cancer cases [2], while low-penetrance genes together with endogenous and lifestyle factors are likely to account for a higher proportion of breast cancer cases [3]. The gene discussed is BRCA1; the disease is breast cancer.