CA-125 Tumor Marker

James Metz, MD
Abramson Cancer Center of the University of Pennsylvania
Last Modified: November 1, 2001

CA-125 is a blood test that is typically used in the management of patients with ovarian cancer. The CA-125 level can be elevated above the normal level in a variety of other conditions besides ovarian cancer. Because most patients with ovarian cancer have an elevated CA-125 level, it is a good test to use to follow response to a particular treatment (the value decreases if a treatment is working or increases if the tumor is growing).

It was hoped that the CA-125 blood test could also be applied as a screening test to detect ovarian cancer at an early stage in women. A good screening test needs to be safe, specific (elevated only from the particular condition being screened), and make a difference in survival because it allows for early initiation of treatment. A number of studies with many thousands of patients have not shown a benefit to using CA-125 as a screening test for the following reasons:

A number of common benign conditions cause an increase in CA-125 including normal menses, pregnancy, fibroids, endometriosis, and pelvic inflammatory disease
Non-gynecologic conditions that elevate the CA-125 level include pancreatitis (inflammation of the pancreas), liver cirrhosis, recent abdominal surgery, and radiation therapy treatments
Other malignant tumors such as breast, lung, colon, and pancreas can increase the CA-125

Because so many other conditions can elevate the CA-125 level, this test has a significant number of false positive results (i.e., it is not very specific). If every patient with a positive result underwent additional work-up, many patients would require a surgical exploration of the abdomen to definitively rule out a diagnosis of ovarian cancer. Surgery can cause significant side effects and even rarely death. It also turns out studies have shown no impact on the rate of death by using the CA-125 as a screening test. Thus, as a screening test in a patient without a diagnosis of ovarian cancer or strong suspicion of its presence, CA-125 does not fulfill the important requirements of a screening test. The risks do not outweigh the benefits, the test is not very specific in its diagnosis, and it has not been shown to significantly impact survival.

Routine screening of asymptomatic patients with a CA-125 level is not currently recommended. There are however individual instances where getting a CA-125 test is prudent. Some physicians still favor the test in patients with a strong family history of ovarian cancer and combine screening for ovarian cancer with pelvic and ultrasound examinations. Regular CA-125 blood tests are clearly indicated in patients previously diagnosed with ovarian cancer to follow response of treatment or catch a recurrence at an early stage.