CA199, the glycoantigen CA19-9, is a mucin tumor marker. It is often used clinically as an aid in the diagnosis of tumor or non-tumor diseases. Some benign lesions can also show high CA19-9, so it is usually not used as a separate diagnostic criterion and needs to be combined with other tests to improve diagnostic accuracy, and there is no special distinction between men and women. I. Benign lesions 1. Gynecological diseases: endometriosis is often measured by combined serum CA19-9 and CA125, which are elevated at the same time to assist in diagnosis; uterine fibroids, ovarian chocolate cysts, pelvic inflammatory disease, ovarian plasmacytic cystadenoma, cervicitis, vaginitis and other diseases may be accompanied by high serum CA19-9, and patients are advised to further improve the examination; 2. Other diseases: serum CA19-9 helps to make dynamic observation of the condition of cirrhotic patients and alert to the occurrence of hepatocellular carcinoma. Active cooperation with CT, MRI and other tests will help early diagnosis and treatment of liver cancer. In addition, diseases such as hepatitis, gallstones, pancreatitis, gastroenteritis, as well as diabetes and renal insufficiency may cause high serum CA19-9, which may also be transiently elevated and therefore cannot be used as a direct diagnostic basis. Malignant lesion 1, gastrointestinal tumor: serum CA19-9 is a more rational marker for pancreatic cancer, and it can also detect recurrence, with high sensitivity and specificity, but it is usually not used as a separate reference basis. In addition, diseases such as liver cancer, stomach cancer, colorectal cancer and biliary tract cancer may also cause significant elevation of serum CA19-9, but the positive rate of stomach cancer and liver cancer is relatively low; 2. Other tumors: ovarian cancer, breast cancer, lymphoma, lung cancer and many other diseases cause high CA19-9, but it is usually combined with alpha-fetoprotein (AFP) and carcinoembryonic antigen (CEA) to help improve the diagnosis rate.