Normal carcinoembryonic antigen does not completely exclude cancer, because carcinoembryonic antigen is not specific and can be elevated in some malignant tumors, such as colon malignant tumors and lung cancer. However, not all malignant tumors of the colon or lung are abnormal, but they may also be normal. For other malignant tumors, this index is usually normal, so it is not possible to diagnose cancer or the absence of cancer based on carcinoembryonic antigen. Besides carcinoembryonic antigen, other commonly used tumor markers such as AFP and CA199 are more frequently used. If AFP is high, primary liver cancer may be considered, and CA199 is usually higher in pancreatic cancer. By the same token, if these tumor markers are normal, cancer in the corresponding area cannot be ruled out. Generally, cancer can only be diagnosed by imaging and further pathological examination.