Question

CA 19-9.

Hint:

CA 19-9 is useful for monitoring and detecting recurrence of certain cancers, but its use as a diagnostic tool is limited by false positives and negatives.

Answer 1

CA 19-9 is a carbohydrate antigen and is a tumor marker primarily used to monitor the progression of pancreatic, colorectal, and biliary tract cancers, particularly cholangiocarcinoma.
Step 1: Clinical Role:
1. Detection of Malignancy: Elevated levels of CA 19-9 are often associated with gastrointestinal cancers, especially pancreatic cancer, but also cholangiocarcinoma and colorectal cancer. However, it is not specific to cancer and can be elevated in benign conditions such as pancreatitis or liver disease.
2. Monitoring Therapy: It is most commonly used in monitoring the effectiveness of treatment, such as chemotherapy, and in detecting recurrence of malignancy after treatment.
Step 2: Limitations:
1. False Positives: CA 19-9 levels can also be elevated in non-cancerous conditions, including liver cirrhosis, pancreatitis, and cholestasis.
2. False Negatives: Some individuals, especially those with a rare blood type (Le(a-b-)), may not produce CA 19-9 even in the presence of a malignancy.