Approximately 15% to 20% of the familial aggregation of breast cancer is accounted for by mutations in high-penetrance susceptibility genes [1-3], such as BRCA1 and BRCA2. Pathogenic mutations in BRCA1 and BRCA2 confer lifetime breast cancer risk of 60% to 85% [4,5] and 40% to 85% [4,5], respectively. The gene discussed is BRCA1; the disease is breast cancer.