BRCA1 and breast cancer: It is estimated that BRCA1 and BRCA2 are responsible for 5 – 10% of breast cancer cases (King et al, 1993; Eeles, 1996) and 10% of ovarian cancer cases (Easton et al, 1993; Couch and Weber, 1998; Landis et al, 1999; Risch et al, 2001).