Several genes predisposing to early-onset breast cancer have been identified, most notably BRCA1 and BRCA2. Carriers of the BRCA1 and BRCA2 mutations face a lifetime risk of breast cancer of over 80% (Easton et al, 1995; Tonin et al, 1995; Ford et al, 1998), although lower numbers have been reported (Streuwing et al, 1997; Antoniou et al, 2003). This evidence concerns the gene BRCA1 and breast cancer.