CHEK2 and breast cancer: The intrinsic factors are not avoidable and are associated with genetic and epigenetic characteristics [5], including mutations in autosomal dominant genes, such as breast cancer 1 (BRCA1) and breast cancer 2 (BRCA2) [6]; mutations in moderate-risk genes, such as the CHK2 serine/threonine protein kinase gene (CHEK2), the ataxia telangiectasia gene (ATM), and the partner and localize of BRCA2 gene (PALB2); or low-frequency variations, such as single-nucleotide polymorphisms (SNPs).