CHEK2 and breast cancer: So far, germline variants in about 10 susceptibility genes have been confirmed to be involved in tumorigenesis and increase the BC risk, mainly including genes involved in DNA repair (BRCA1, BRCA2, ATM, CHEK2, PALB2, BARD1, RAD51C, and RAD51D) and genes caused pleiotropic tumor syndromes (TP53, CDH1, PTEN, STK11, and NF1) [5,6].