CHEK2 and breast cancer: Mutations in other genes causing familial syndromes in which BC incidence is highly increased (TP53, PTEN, STK11 and CDH1) are estimated to cause 5 % of the familial forms of BC and an additional 5 % is accounted for by moderate penetrance genes (i.e. associated with an odds ratio (OR) below 3), such as ATM, CHEK2, and the Fanconi anemia pathway genes (BRIP1, PALB2, RAD51C, RAD51D and XRCC2).