CA 19-9 is a marker for which of the following: September 2011
**Core Concept**
CA 19-9 is a tumor marker that is primarily used to monitor the treatment response and detect recurrence in pancreatic cancer. It is a type of mucin glycoprotein that is produced by the mucous cells of the pancreas and other tissues.
**Why the Correct Answer is Right**
CA 19-9 is elevated in patients with pancreatic cancer, particularly in those with adenocarcinoma, which is the most common type of pancreatic cancer. The CA 19-9 antigen is a carbohydrate moiety that is expressed on the surface of cancer cells and is shed into the blood, where it can be measured using a serum test. Elevated levels of CA 19-9 are also seen in other conditions, such as cholangiocarcinoma, gastric cancer, and colorectal cancer, but pancreatic cancer is the primary association.
**Why Each Wrong Option is Incorrect**
**Option A:** CA 19-9 is not primarily used as a marker for lung cancer, although some studies have shown elevated levels in a subset of patients with non-small cell lung cancer.
**Option B:** While CA 19-9 is a tumor marker, it is not primarily used to monitor the treatment response and detect recurrence in breast cancer.
**Option C:** CA 19-9 is not a marker for ovarian cancer, which is typically associated with elevated levels of CA-125.
**Clinical Pearl / High-Yield Fact**
It's essential to note that CA 19-9 is not a specific marker for pancreatic cancer, as elevated levels can also be seen in other conditions. However, a significant elevation in CA 19-9 levels in a patient with symptoms suggestive of pancreatic cancer can help support the diagnosis.
**Correct Answer: C. Pancreatic cancer**