CHEK2 and breast cancer: On the other hand, the majority of gens can be categorized as moderate-penetrant genes in most of the breast cancer cases including CHEK2, ATM, CDH1, NBS1, BRIP1, PALB2, BARD1, RAD50, and RAD51, which are frequently mutated in the general population and contribute in developing of breast cancer [3, 10, 11].