What is carcinoembryonic antigen Carcinoembryonic antigen (CEA) is an acidic glycoprotein with the characteristics of human embryonic antigen, which exists on the surface of cancer cells differentiated from endodermal cells and is a structural protein of cell membrane. The clinical value of carcinoembryonic antigen is mainly found in the fetal gastrointestinal duct, pancreas and liver during embryonic period, and the content in tissues is very low after birth. Elevated serum carcinoembryonic antigen is seen in malignant tumors of the gastrointestinal tract, and also in the serum of breast cancer, lung cancer and other malignant tumors. Therefore, carcinoembryonic antigen is a broad-spectrum tumor marker, and although it cannot be used as a specific indicator for the diagnosis of certain malignant tumors, it still has important clinical value in the differential diagnosis, disease monitoring and efficacy evaluation of malignant tumors. Normal carcinoembryonic antigen is secreted into the gastrointestinal tract, while carcinoembryonic antigen secreted by cancer cells that have lost polarity enters the blood and lymphatic fluid, so it is increased in the blood. Clinical significance of carcinoembryonic antigen Usually, the reference value of CEA is <5ug/L (enzyme-linked immunoassay). CEA can be expressed in some adult tumor tissues, including embryonic tumors, colon, stomach, lung, breast and other cancer tissues, and secreted in body fluids, etc. CEA is only significantly elevated in the middle and late stages of tumors, and is not limited to a certain type of tumors, so CEA is not helpful for early detection and differential diagnosis of most tumors; CEA has high false positives and false negatives, and is not suitable for tumor CEA has high false-positive and false-negative properties, and is not suitable for general investigation of tumors. Throughout the treatment of colorectal cancer, CEA is an effective surveillance indicator and an ideal indicator to detect recurrence, and its sensitivity is higher than that of X-ray and proctoscopy. CEA is important for the assessment of prognosis of certain tumors: patients with normal preoperative CEA level have a high surgical cure rate and are less likely to recur after surgery; if CEA is already elevated before surgery, most of them have invasion and metastasis in the vascular wall, lymphatic system and peripheral nerves and have a poor prognosis; after surgery, if the cancer has metastasis or recurrence, CEA may start to increase 10 weeks to 13 months before the appearance of clinical symptoms. The change of CEA concentration increases with disease progression. When making tumor diagnosis, benign diseases with CEA elevation should be excluded: smokers; ulcerative colitis; pancreatitis; colonic polyps, etc.