Carcinoembryonic antigen (CEA) is a protein synthesized in the gastrointestinal tract, liver and pancreas during embryonic life. Carcinoembryonic antigen is a broad-spectrum tumor marker that reflects the presence of many tumors to people, and is a better tumor marker for judging the efficacy, disease progression, monitoring and prognosis estimation of colorectal cancer, breast cancer and lung cancer. I. What is carcinoembryonic antigen? Carcinoembryonic antigen is an acidic glycoprotein with human embryonic antigenic determinant cluster. It is a broad-spectrum tumor marker mainly found in organs such as gastrointestinal tract, liver and pancreas during embryonic period and at very low levels after birth. The digestive tube and certain tissues in early fetal life contain the ability to synthesize CEA, but the amount decreases gradually after the sixth month of pregnancy and is extremely low after birth. However, abnormally high levels of CEA can be found in the serum of patients with certain malignant tumors. It has significance for the diagnosis of tumors and the determination of prognosis and recurrence. Its serum concentration is associated with many kinds of tumors, especially gastrointestinal tumors, and the positive detection rate is in the order of colon cancer, rectal cancer, gastric cancer, pancreatic cancer, bile duct cancer, etc. Malignant tumors of lung, breast and genitourinary system are also elevated. The determination of carcinoembryonic antigen is mainly used for differential diagnosis, disease surveillance and efficacy judgment of tumors. Normal value of carcinoembryonic antigen Enzyme-linked immunosorbent assay: <5μg/L. Monoclonal antibody solid phase enzyme assay: <3μg/L normal. 3-5μg/L suspicious. >5μg/L positive. Clinical significance of carcinoembryonic antigen Carcinoembryonic exists in antigenic major rectal and colon cancer tissues and fetal intestinal mucosa, and the index is significantly elevated in colon cancer, gastric cancer, lung cancer and bile duct cancer. It also exists in the tumor tissues of liver cancer, pancreatic cancer, kidney cancer, breast cancer, esophageal cancer, ovarian cancer, etc. CEA produced by cellular secretion enters local body fluids and blood, therefore, abnormal increase of CEA can be found in serum, chest and ascites, and digestive fluid of the above cancers. CEA in pleural fluid of lung cancer is often higher than that in serum. The normal reference value of CEA varies slightly depending on the method. There is no gender difference in its level, but it increases slightly with age. There is a mild increase in smokers. In primary colorectal cancer, the CEA positive rate is about 45% to 80% in early stage without metastasis, and the concentration and positive detection rate of CEA are higher in patients with metastasis. Some literature reports that the positive rate of pancreatic and biliary tract tumors can reach 60% to 70%, and the positive rate of gastric cancer and lung cancer is about 50%. Elevated CEA can also be seen in sclerosing hepatic ductitis. In other diseases such as benign tumors, inflammatory and degenerative diseases (colon polyps, ulcerative colitis, pancreatitis, alcoholic hepatic steatosis, active liver disease, etc.) the level can also be increased in some patients, but the value is much lower than in malignant diseases, generally less than 20 μg/L. For some cases that are difficult to identify, dynamic observation can be done, and the value gradually increases or continues to be high, the possibility of benign is less. When ovarian cysts are present and the nature of the cysts cannot be confirmed, this test can be done to rule out malignant ovarian tumors. Hint: The specificity is not strong, the sensitivity is not high, and the effect on early diagnosis of tumor is not obvious. It can return to normal value 6 weeks after surgical removal of the tumor, otherwise, it suggests the presence of residual tumor. However, there are false positives exist, for example, long-term smokers may have false positives.