Hereditary breast cancer is also caused by pathogenic variants in other well-reported susceptibility genes such as ATM, CDH1, CHEK2, PALB2, PTEN, TP53, and NF1. CHEK2 (cell cycle checkpoint kinase 2) is a moderately penetrant breast cancer susceptibility gene which can increase the breast cancer risk by two to threefold [16–18]. The gene discussed is CHEK2; the disease is breast cancer.