Although heterozygous germ-line mutations in the BRCA1/2 genes render a risk of up to 85% for the development of breast cancer, and 10–40% for ovarian cancer, only a small fraction of tumors are BRCA-deficient, accounting for 3–5% of all breast cancers and 15% of ovarian cancers (8,9). The gene discussed is BRCA1; the disease is breast cancer.