The genetic susceptibility to BC is determined by rare high-penetrance variants in BRCA1, BRCA2, PALB2, and TP53 [9,10,11], likewise rare moderate-risk variants (e.g., in ATM, CHEK2, and RAD51C) [12], as well as common low-risk variants, predominantly single nucleotide polymorphisms (SNPs) [13,14]. Here, CHEK2 is linked to breast cancer.