Carcinoembryonic antigen (CEA), a tumor-associated antigen first extracted from colon cancer and embryonic tissue by Gold and Freedman in 1965, is an acidic glycoprotein with human embryonic antigen properties that is present on the surface of cancer cells differentiated from endodermal cells and is a structural protein of the cell membrane. It is formed in the cell plasma, secreted outside the cell through the cell membrane, and then enters the surrounding body fluids. Therefore, it can be detected from a variety of body fluids and excreta such as serum, brain crest fluid, breast milk, gastric fluid, chest and abdominal fluid, and urine and feces. The normal value of carcinoembryonic antigen is ≤5ng/ml. Clinical significance of carcinoembryonic antigen: carcinoembryonic antigen is not a specific marker of malignant tumor, so it has only auxiliary value in diagnosis. Elevated CEA is commonly found in colorectal cancer, pancreatic cancer, gastric cancer, breast cancer, medullary thyroid cancer, liver cancer, lung cancer, ovarian cancer, and urological tumors. However, smoking, pregnancy and cardiovascular diseases, diabetes, intestinal diverticulitis, rectal polyps, colitis, pancreatitis, cirrhosis, hepatitis, and pulmonary diseases, etc. Serum CEA is also elevated in 15% to 53% of patients, so CEA is not a specific marker for malignant tumors. In addition, the level of carcinoembryonic antigen is related to the following factors: ①related to the early, middle and late stages of cancer, the more advanced the carcinoembryonic antigen value increases, but the positivity rate is not very high. ②Related to tumor metastasis, when the metastasis, the concentration of carcinoembryonic antigen also increases. ③Related to the tissue type of cancer, adenocarcinoma is the most sensitive, followed by squamous carcinoma and hypofractionated carcinoma, which indicates that carcinoembryonic antigen is a differentiated antigen, and the higher the differentiation degree, the higher the positive rate. The concentration of serum carcinoembryonic antigen decreases when the disease improves and increases when the disease deteriorates. The continuous follow-up test of carcinoembryonic antigen can be used to observe the efficacy and prognosis of malignant tumors after surgery, and can also be used to observe the efficacy of chemotherapy patients. A high value of carcinoembryonic antigen does not necessarily indicate cancer, as its specificity is not strong, sensitivity is not high, and its role in early diagnosis of tumors is not obvious. When carcinoembryonic antigen (CEA) is high, you can start from the following points: 1. go to the hospital for a comprehensive cancer prevention physical examination; 2. monitor carcinoembryonic antigen dynamically; 3. ask an oncologist for a physical examination and comprehensive analysis of the relevant laboratory results of gastric cancer carcinoembryonic antigen (CEA). Carcinoembryonic antigen is an acidic protein. Normal mucosa next to cancer has little or negative CEA. The CEA positivity rate of gastric cancer was 85.58%. Among them, 100% were mucinous adenocarcinoma and indolent cell carcinoma (mucinous cell carcinoma). Electron microscopy showed that CEA was distributed in both the cancer cell membrane and the organelles of protein synthesis and transport (such as nuclear membrane, endoplasmic reticulum, Golgi apparatus and its secretory vesicles) in the cytoplasm of cancer cells, suggesting that the synthesis of CEA by cancer cells increased, and therefore the CEA entering the glandular lumen also increased, and the concentration of CEA in body fluid and gastric fluid was higher than that in serum because CEA was located in the sugar envelope around the cell membrane and could be easily released into the surrounding body fluid. The reason for the higher CEA content in the plasma of cancer cells is related to the increased synthesis of CEA in cancer cells and the blocked excretion of CEA. When cancer cells become degenerative and necrotic, the intracellular membrane structure is damaged and ruptured, and CEA can appear in the cytoplasmic matrix. The CEA antigen determinant is glycoprotein, and the infiltration and metastasis of tumor cells are related to the glycosylation of cell membrane glycoprotein. In addition, mucinous cell carcinoma can also secrete and release a large amount of protein hydrolase, which can destroy the calcium bridge of cancer cells and dissolve the soft tissue around the cancer nest. Therefore, gastric mucinous cell carcinoma is highly invasive and has a high metastasis rate.