Some lung cancers, such as intestinal lung adenocarcinoma, have elevated CA199. CA199 is a glycoprotein, and its obvious elevation is seen in pancreatic cancer, hepatobiliary and gastrointestinal diseases, which is not closely related to lung cancer, but some intestinal lung adenocarcinomas can also be seen with elevated CA199. At present, it is generally believed that CA199 is the tumor marker of choice for pancreatic cancer, with high specificity and sensitivity for the early diagnosis of pancreatic cancer. Usually, CA199 is measured together with CEA (carcinoembryonic antigen), which can help to improve its sensitivity in the diagnosis of pancreatic and gastric cancers, and its positive rate in the diagnosis of gallbladder and bile duct cancers is about 85%. Patients with elevated CA199 should be continuously monitored, which is of great value in the evaluation of their disease progression, surgical efficacy and prognosis, and should be actively diagnosed and treated when obvious abnormalities occur.