BRCA2 and breast cancer: However, despite the high penetrance and the high frequency of variants found in BRCA1/BRCA2 genes, only about 20% of hereditary BC and OC have been attributed to the presence of pathogenic variants in those genes, moreover, about 5–10% have been associated with other susceptibility genes, such as TP53, STK11, PTEN, ATM, and CHEK2 [14].