Mutations in some moderately penetrant and rare genes such as checkpoint kinase-2 (CHEK2), BRCA1-interacting protein-1 (BRIP1), ataxia telangiectasia mutated (ATM), and partner and localizer of BRCA2 (PALB2) are also involved in the development of BC in a minority of cases (2 to 3%) [35]. The gene discussed is CHEK2; the disease is breast cancer.