The prevalence of familial cases indicates that about 10% of all breast cancers are heritable (Rowell et al, 1994), but major mutations such as BRCA1, BRCA2, and TP53 can only be a minority of these (Cui et al, 2001b; Peto et al, 1999); familial cases are especially prominent before menopause (Pharoah et al, 1997). Here, BRCA1 is linked to breast cancer.