With the substantial increase in knowledge of cancer genetics (8, 9), more than 30 potential breast cancer susceptibility genes (BCSGs) have been suggested, including genes with high (e.g., BRCA1/2, TP53, CDH1, PTEN, and STK11), moderate (e.g., PALB2, CHEK2, ATM, and RECQL), and low-to-disputed penetrance (e.g., MLH1, MSH2, MSH6, PMS2, MEN1, and PPM1D) (9–12). The gene discussed is CHEK2; the disease is breast cancer.