ADA and esophageal squamous cell carcinoma: When compared to NAT, tumor tissues of ESCC exhibited significantly abundant expression in the metabolites, including hypoxanthine, xanthine, adenine, adenosine, etc. Some genes had significantly upregulated expression, including HPRT1, IMPDH1, GDA, ADA, etc. The downstream metabolites guanosine monophosphate and deoxyadenosine monophosphate had significantly increased levels.