BRCA1 and breast cancer: An extrapolation of the present results in an effort to deduce the true frequency of all BRCA1 and BRCA2 mutations in unselected breast cancer patients would suggest that about 4.8% of all Greek breast cancer patients can be carriers of a BRCA1 or BRCA2 mutation, as the four mutations screened here (2.6% frequency) only represent 54% of the BRCA1/2-positive high-risk families.