About 5–10% are the so-called familial cases, which can be mainly attributed to deleterious mutations in BRCA1 and BRCA2 (Dunning et al, 2001; Nathanson and Weber, 2001), and also for the remaining majority of spontaneous breast cancer cases a strong genetic component has been postulated (Lichtenstein et al, 2000). Here, BRCA1 is linked to breast cancer.