The determination of tumor markers can be used as one of the contents of screening (currently often included in personal physical examination programs) and has a certain reference value for the diagnosis of tumors. It can also observe the treatment effect of tumor, monitor recurrence, metastasis and judge the prognosis. Commonly used GI tumor markers include CEA (carcinoembryonic antigen), CA199, CA125, CA50, CA242, CA724. clinically, patients suspected of esophageal cancer are preferred to test CA199, followed by CEA. patients suspected of gastric cancer are preferred to test CEA and CA724, followed by CA199 and CA242. patients suspected of colon cancer are preferred to test A single abnormality of the above markers often lacks clear specificity, and a significant increase in multiple markers at the same time is of greater clinical significance, but can only be used as a reference for clinical diagnosis.