Carcinoembryonic antigen (CEA) is a common tumor marker that may be normal in normal tissues but may also be normal in malignant tumors, and not all malignant tumors have abnormal CEA. In general, CEA may be more elevated in colon malignancies and lung malignancies, but may be normal in other malignancies. Even in colon cancer and lung cancer, if the disease is relatively stable, the carcinoembryonic antigen may be normal. Therefore, whether or not the carcinoembryonic antigen is normal alone cannot diagnose the presence or absence of cancer or the development of the disease, and other imaging and endoscopic examinations are needed.