CHEK2 and Hereditary breast and ovarian cancer syndrome: In addition to BRCA1/2, several other non-BRCA genes are associated with hereditary breast and ovarian cancer (HBOC) syndrome and have been identified, including highly penetrant genes such as PTEN, TP53, CDH1, and STK11 and moderate penetrant genes like ATM, CHEK2, PALB2, BRIP1, BARD1, RAD51C, and RAD51D.