Carbohydrate Antigen 19-9 (CA 19-9)

CA 19-9 is an antigen produced by pancreatic, biliary and gastrointestinal cells. It is most commonly used to monitor response to therapy and disease progression in patients with pancreatic adenocarcinoma.
An increase in CA19-9 during treatment may indicate that the cancer is not responding well to therapy, while a decrease may indicate a positive response.

It is also useful for detecting recurrence after surgery or other treatments, such as chemotherapy.

High levels of CA 19-9 at diagnosis are often associated with a poor prognosis and advanced disease.

CA 19-9 is also used in the diagnosis and monitoring of cholangiocarcinoma. CA 19-9 levels can be elevated in other malignancies, including colorectal cancer, gastric cancer, hepatocellular carcinoma (liver cancer) and gallbladder cancer.

Elevated CA 19-9 levels can also be observed in non-cancerous conditions, particularly those affecting the liver, pancreas or biliary system. 

This lack of specificity means that elevated CA 19-9 levels are not always indicative of cancer and should be interpreted with caution, particularly in the context of underlying benign disease.