Mutations in DNA repair genes (e.g., BRCA1/2, PALB2, and RAD51C) and genome gatekeeper genes (e.g., TP53, ATM and CHEK2) are frequently found in cancer [212,213], and cancer cells with defective DDR or cell cycle checkpoints replicate damaged DNA to meet the uncontrolled proliferative drive induced by oncogenic signals. The gene discussed is CHEK2; the disease is cancer.