Cancer may exist within the normal range of carcinoembryonic antigen because carcinoembryonic antigen is not specific and some tumors are not elevated, such as glioma, prostate cancer, and small cell lung cancer. Elevated carcinoembryonic antigen is commonly found in colorectal cancer, gastric cancer, breast cancer, pancreatic cancer, lung cancer, ovarian cancer and medullary thyroid cancer, etc. However, rectal polyps, colitis, pancreatitis, cirrhosis of the liver, and diabetes mellitus and smoking, lung disease, etc., a part of the patients will be elevated, carcinoembryonic antigen is not a specific marker of malignant tumors, but only an auxiliary diagnostic value. Furthermore, the level of carcinoembryonic antigen is also related to the early, middle and late stages of cancer, the more advanced the stage, the higher the carcinoembryonic antigen. It is also related to the tissue type of the cancer, with adenocarcinoma being more sensitive, followed by squamous cell carcinoma and poorly differentiated carcinoma. In addition, carcinoembryonic antigen is elevated later than the clinical tumor. Whether there is a tumor or not is recommended to have regular medical checkups to comprehensively determine whether there is a tumor or not, and to go to the hospital in time for a clear diagnosis and treatment, so as to avoid delaying the condition.