The prevalence of BRCA1 and BRCA2 mutations were reported in 2.5–3.1% for sporadic breast cancers, in 19.4–42.9% for familial breast cancer patients with two or more affected first- and second-degree relatives with breast or ovarian cancers, and in 9.6–18.3% for early onset breast cancers. Here, BRCA1 is linked to breast cancer.