For instance, ALDH2, which is important for acetaldehyde (a metabolite of ethanol and an ingredient in tobacco smoke) metabolism and whose deficiency increases the risk for esophageal and head and neck SCCs, was found to be relatively downregulated in ESCC and LUSC, but was not significantly different when comparing ECA and CESC (Fig 7E). This evidence concerns the gene ALDH2 and esophageal squamous cell carcinoma.