BRCA1 and breast cancer: In contrast, BRCA1 mutations are rare in sporadic breast cancer, suggesting that BRCA1 is inactivated by nonmutational mechanisms (Papa et al, 1998), since epigenetic mechanisms (e.g. promoter hypermethylation), manifested as abnormal expression, have been shown to be involved in abrogating the function of certain tumour suppressor genes (such as BRCA1), which are already targeted by LOH (Dobrovic and Simpfendorfer, 1997; Jones and Baylin, 2002).