BRCA1 and breast cancer: Germline mutations in BRCA1 or BRCA2 explain about 50 % of disease aggregation in severely affected BC and OC families while their prevalence is lower among BC and OC patients unselected for family history or age of diagnosis: BRCA1 mutations are found in <1–7 % cases and BRCA2 mutations in 1-3 % cases [5].