Tumor markers of the GI tract mainly include: 1. Carcinoembryonic antigen, the most important GI tumor marker, with a normal value of less than 3.45 μg/L, is elevated in colon cancer, rectal cancer, esophageal cancer, gastric cancer, and pancreatic cancer, especially in colon cancer. 2. Glycoantigen 199, with a normal value of less than 27 U/ml, is significantly elevated in colon cancer and rectal cancer, but is also slightly elevated in GI inflammation. 3. The normal value of glycoconjugate antigen 125 is less than 35 U/ml, which is significantly elevated in gastrointestinal malignancies. 4. glycoconjugate antigen 724 is less than 6.9 U/ml, which is significantly elevated in gastric cancer. 5. glycoconjugate antigen 50 is less than 20 μg/L, which is significantly elevated in colorectal cancer.