CHEK2 and breast cancer: More recently, 13% of patients with BC were found to harbor germline variants, 75% of which were located in DDR genes, mainly in BRCA2, mutS homolog 2 (MSH2), BRCA1, checkpoint kinase 2 (CHEK2), ERCC excision repair 3 (ERCC3), nibrin (NBN), and RAD50 double strand break repair protein (RAD50) [19].