CHEK2 and breast cancer: The HBOC gene panel includes 12 genes that are both high-risk genes, i.e., a four times higher risk of BC (BRCA1, BRCA2, PALB2, CDH1, PTEN, STK11 and TP53), and moderate-risk genes, i.e., a two to four times higher risk of BC (BARD1, CHEK2, RAD51C, RAD51D and ATM) (Table 1) (Figure 1) [3,5,6,7,8].