CA 125 is a protein found on the surface of many cancer cells (ovarian, pancreatic, breast, lung, colorectal, etc.) and normal cells. High CA 125 levels are found in 80% of ovarian cancer cases and in varying percentages of other cancers. Moderately high CA 125 levels are also found in a large number of benign conditions including menstruation, pregnancy, endometriosis, cirrhosis of the liver, peritonitis and acute pancreatitis, etc. For this reason, CA 125 testing is not recommended in asymptomatic individuals unless there is a pelvic mass on ultrasound or a family history of ovarian cancer (BRCA1 or BRCA2 gene mutation).
A decrease in CA 125 levels during the treatment of ovarian cancer is one indication (but not the only one) of a favourable response to treatment, whereas a renewed increase after treatment may be a sign of the disease’s recurrence.
CA 125 levels can vary depending on the testing technique used. It is therefore important to always have testing done in the same laboratory. Some people have antibodies in their blood called “heterophile antibodies,” which may interfere with CA 125 testing.