1.carcino-embryonic antigen CEA Carcino-embryonic antigen is a glycoprotein produced by colorectal cancer tissues, which can cause immune response of patients as an antigen. This antigen is called carcino-embryonic antigen CEA, which can be widely present in endodermal origin of digestive system cancer, and also in normal embryonic digestive tract tissue, and can also exist in trace amounts in normal human serum. CEA is a broad-spectrum tumor marker, which can reflect the existence of many kinds of tumors. It is a good tumor marker for judging the efficacy, disease development, monitoring and prognosis estimation of colorectal cancer, breast cancer and lung cancer, but its specificity is not strong, sensitivity is not high, and its role in early diagnosis of tumors is not obvious. 2.Introduction of carcinoembryonic antigen CEA Carcinoembryonic antigen was initially found in colon cancer and fetal intestinal tissue, hence the name. Elevated serum CEA is not only seen in GI tract cancer, but also in other systems. Continuous monitoring of carcinoembryonic antigen levels can be used to observe the efficacy of tumor treatment and determine the prognosis. Generally, the level of serum carcinoembryonic antigen decreases when the disease improves and increases when the disease progresses. The clinical significance of carcinoembryonic antigen CEA (1) Elevated CEA is commonly found in colorectal cancer, pancreatic cancer, gastric cancer, breast cancer, medullary thyroid cancer and so on. But smoking, pregnancy and cardiovascular diseases, diabetes, non-specific colitis and other diseases, 15%~53% of patients’ serum CEA will also be elevated, so CEA is not a specific marker for malignant tumor and only has an auxiliary value in diagnosis. In addition, there is a clear relationship between serum CEA level and the stage of colorectal cancer, the more advanced the lesion, the higher the CEA concentration. (2) 97% of healthy adults have serum CEA concentrations below 2.5 ng/mI. Increased CEA accounts for 45-80% of patients with primary colon cancer. In addition to primary colon cancer, pancreatic cancer, bile duct cancer, gastric cancer. Esophageal cancer, adenocarcinoma, lung cancer, breast cancer and tumors of the urinary system also have a high positive rate, generally at 50-70%. (3) Benign tumors, inflammatory and degenerative diseases, such as colon polyps, ulcerative colitis, pancreatitis and alcoholic cirrhosis change patients also have partially elevated CEA, but much lower than malignant tumors, generally less than 20 μg/L. CEA over 20 μg/L often indicates the presence of gastrointestinal tumors. Therefore, the determination of CEA can be used as a basis for differential diagnosis between benign and malignant tumors. Detection of carcinoembryonic antigen CEA Carcinoembryonic antigen (CEA), first reported by Gold and Freedman in 1965, was extracted from liver metastases of colon adenocarcinoma and normal fetal gastrointestinal tract. It is considered to be one of the most widely used human tumor-associated antigens. As an immune heterogeneous glycoproteome, CEA has a molecular weight of roughly 200,000 daltons and contains 50-85% carbohydrates . CEA is a member of the immunoglobulin family and exhibits the function of binding intercellular molecules. In addition, substances related to the molecular structure of CEA (e.g. NCA, NCA-2, NFA) have been reported in normal human tissues. The determination of CEA in serum shows potential advantages in the diagnosis and treatment of malignancies, especially colon adenocarcinoma. Post-treatment follow-up can be used to monitor the progression, degeneration and recurrence of the patient’s tumor. A persistent increase in CEA after drug or surgical treatment is often a sign of residual or recurrent tumor, and a decrease in concentration to the normal range is a sign of successful treatment. Elevations are also seen in patients with non-malignant disease or in heavy smokers; therefore, CEA should not be used as a screening indicator for diagnosing cancer or in asymptomatic patients.