CA 19-9 (Cancer Associated Antigen 19-9)

CA 19-9, equivalent to Sialyl Lewis a antigen, is a mucin type glycoprotein found in the blood repetitively bearing a carbohydrate epitope which is specifically recognized by the mouse monoclonal antibody, C192. CA 19-9 is an oncofetal antigen, expressed by several different cancers, but especially carcinomas of the gastrointestinal tract. It is present in the fetal epithelium of the stomach, intestine, liver and pancreas. CA 19-9 is a tumor marker for pancreatic, gallbladder, gastric and colorectal cancers. CA 19-9 can be used to track treatment progress of previously diagnosed cancer. This blood test in conjunction with periodic CT scans will show whether the cancer is in remission or is continuing to grow. However, it is more useful in measuring the effectiveness of cancer treatment by studying the patient’s CA 19-9 levels over time. There are benign diseases of the bile ducts and pancreas that occasionally result in elevated CA 19-9 levels and a low CA 19-9 level does not exclude the possible presence of a malignant tumor. For this reason, the determination of CA 19-9 concentrations is not considered as a diagnostic test.