CEA, also known as carcinoembryonic antigen, has a normal value of 10 U/ml or less. CEA is a tumor marker that indicates the presence of gastrointestinal tumors or lung adenocarcinoma. If the value of carcinoembryonic antigen is significantly elevated, one should be careful if there is a combination of gastrointestinal tract tumor, such as gastric cancer, intestinal cancer, pancreatic cancer, etc. or lung adenocarcinoma, and CT scan of the lung and CT scan of the whole abdomen with enhancement should be done to find out if there are occupying lesions in these areas. If so, further gastroscopy, colonoscopy, or aspiration biopsy of the pancreatic mass is required for clarification. If it is an occupying lesion in the lung, a puncture biopsy of the lung mass or direct radical surgical resection is needed to determine whether it is lung cancer.