CMTM7 and esophageal squamous cell carcinoma: CMTM7, located on chromosome 3p22.3, is a tumor suppressor gene that is downregulated or absent in many cancer types [such as esophageal squamous cell carcinoma (ESCC) and non-small cell lung cancer (NSCLC)] due to promoter hypermethylation and loss of heterozygosity.