The development of molecular genetics last years brought a better understanding of the mechanisms of breast cancer development. "The hereditary" breast cancer is very much connected with the BRCA 1 and BRCA 2 gene mutations. Recent studies suggest a role for BRCA 1 and BRCA 2 in transcriptional regulation, as it possesses a conserved NH2 terminal ring finger domain and an COOH domain. This role would be consistent with the reported localization of the BRCA 1/BRCA 2 protein to the nucleus. The BRCA 1 and BRCA 2 may play an as yet undefined protective role in cells, as it is expressed in epithelial cells undergoing high levels of proliferation in association with differentiation.