Carcinoembryonic antigen(CEA) is an embryonic cancer antigen, belongs to the immunoglobulin superfamily, which normally exists in fetal digestive tract epithelium, liver and pancreas, but occurs at low concentrations in adults. It is widely expressed in various glandular epithelial tumors, especially gastrointestinal epithelial tumors, and most of them are positive for gastrointestinal cancer, pancreatic cancer and lung adenocarcinoma.The antibody is used to used to identify adenocarcinomas of the digestive tract, distinguish between malignant mesothelioma and peripheral pulmonary adenocarcinoma.