MGMT and esophageal squamous cell carcinoma: In ESCC, DNA methylation frequently results in the inactivation of the genes RARβ, RARβ2, CRBP1, and TIG1, which are linked to retinoic acid signaling, and in contrast, another study revealed that RARβ2, p16, MGMT, CLDN3, CRBP, and MT1G were increased in ESCC tissues [171,173].