CA 19.9 (Pancreatic Cancer Marker)

CA 19.9 (cancer antigen 19.9) is a protein found in the blood that can be raised in certain conditions affecting the pancreas and digestive system. It is best known as a tumour marker for pancreatic cancer, where levels are often elevated, and it is used mainly to help monitor the condition rather than to detect it in the first place.

What it can help assess

• Monitoring known pancreatic cancer, by tracking how levels change during and after treatment to help assess response and check for recurrence
• Supporting the investigation of pancreatic and biliary conditions, alongside imaging and other tests
• Following certain other cancers, such as those of the bile ducts, where CA 19.9 may also be raised

An important note on interpretation

CA 19.9 is not a screening or diagnostic test for pancreatic cancer. Levels can be normal in early disease, so a normal result does not rule cancer out, and it should never be used to detect the disease in someone without a diagnosis. Levels can also be raised by a number of non-cancerous conditions, including gallstones, pancreatitis, and other liver and bile duct problems, as well as jaundice. In addition, a small proportion of people do not produce CA 19.9 at all, meaning the marker is not informative for them. For these reasons the result is always interpreted alongside your full clinical picture rather than on its own.

Why it matters

For people diagnosed with pancreatic or related cancers, CA 19.9 is a useful tool for monitoring the condition over time and assessing how well treatment is working. Any result should be discussed with your GP or specialist, who can interpret it in the context of your individual situation and advise on the appropriate next steps.