Carbohydrate antigen 19-9 （CA19-9） is a mucin-type carbohydrate protein tumor marker, which is a glycolipid on the cell membrane and is generally formed by the precursor substances of Lewis antigens （including Le-a and Le-b） under the combined action of sialtransferase and petrosyltransferase. CA19-9 is distributed in normal human pancreatic and bile duct epithelial cells, and exists in the form of salivary mucin in serum, but the content is small. Studies have shown that CA19-9 can trigger the development of pancreatitis by accelerating the overactivation of pancreatic epidermal growth factor receptor （EGFR） signaling, leading to the progression of pancreatitis to pancreatic cancer.
CA19-9 is often used in the clinical diagnosis of pancreatic cancer, and can also be used in the clinical auxiliary detection of gastric cancer, colorectal cancer, gallbladder cancer, bile duct cancer, liver cancer. After tumor resection, CA19-9 concentration will decrease, and if it increases, it can indicate tumor recurrence. However, it should be noted that CA19-9 is also elevated under the influence of many benign diseases, which is difficult to be applied to the screening and early diagnosis of malignant tumors, so it needs to be combined with other indicators, such as: CA19-9, CA125, AFP, CEA, HE4 combined detection for ovarian cancer; Combined detection of CA19-9, SCCA, CYFRA21-1 and NSE levels for diagnosis and treatment of non-small cell lung cancer; CA19-9, β2-MG, PSA combined detection for diagnosis of prostate cancer; Serum CA19-9 and CA15-3 combined with ultrasound can detect breast cancer.