Common genetic variants could also act as modulators of the risk conferred by PVs in the high-penetrance BC susceptibility genes BRCA1 and BRCA2 and, more recently, also in the high-to-moderate penetrance genes PALB2, CHEK2, and ATM [42,144,162,163,164,165,166,167,168]. This evidence concerns the gene CHEK2 and breast cancer.