XRCC6P5 and colorectal carcinoma: Indeed, there are several studies that found an association between vitamin B12 and methylation of key genes in CRC, such as cyclin-dependent kinase inhibitor 2 A (p16), a tumor suppressor gene; and methylguanine methyltransferase (MGMT), a DNA-repairing protein or homeobox A 4 (HOXA 4)—its overexpression leads to CRC [12,36,37].