Carcinoembryonic antigen(CEA)is an acidic glycoprotein complex with antigen properties of human embryos,which is present on the surface of cancer cells differentiated from endoderm cells and is a structural protein of the cell membrane.It is closely related to the pathogenesis of gastrointestinal malignant tumors, such as colorectal cancer, pancreatic cancer,gastric cancer, esophageal cancer, gallbladder cancer, etc., and is also closely related??? to the pathogenesis of extragastrointestinal malignant tumors such as lung cancer,breast cancer, and medullary? thyroid? cancer.