DKK3 and hepatocellular carcinoma: Considering that the methylation of critical genes, such as cell cycle–related genes and tumor suppressor genes, has been reported to initiate the formation of neoplasm (31), and considering that the methylation of DKK3 has been reported to be involved in the initiation of hepatocellular carcinomas (32), the emergence and the predominance of Dkk3-methylated gastric stem cells could be involved in the initiation of aging-related gastric carcinogenesis.