CA-125: What is it and Who is it for?

The CA-125 blood test is primarily used to monitor patients who have ovarian cancer. It helps to see if therapy is working while treatment is ongoing and can help determine if cancer has returned after chemotherapy has been completed.

Repeating the CA-125 at predetermined interval can show rising or falling amounts. Known as serial testing, this will help the oncologist make a adjustment to the treatment plan.

There are four possibilities – the number is rising, the number is falling, the number remains unchanged or the level baseline CA-125 was normal.

If CA-125 levels are falling, this would indicate indicates a good response to treatment. If CA-125 levels are rise or remain the same, then treatment may not be having the desired result. Increasing CA-125 levels after treatment may indicate that the cancer has returned.

If a woman with ovarian cancer has her first CA-125 level and it is normal, then the additional tests are not likely to be helpful in monitoring her ovarian cancer. Not all ovarian cancers are associated with increased levels of CA-125. Elevated levels are found in about 75-80 percent of ovarian cancers.

CA-125 is sometimes suggested for high-risk women who are at risk for ovarian cancer. However, medical studies have not yet proven it to have the desired outcome.

One must understand that CA-125 concentrations can be elevated for reasons other than ovarian cancer. Examples include normal menstruation, pregnancy, endometriosis, bowel disorders and pelvic inflammatory disease.

This test is not used to screen the general population for ovarian cancer. A major research agenda is to find a reliable screening test for ovarian cancer.

Who would most likely benefit from serial CA-125 blood tests?
Women diagnosed with ovarian cancer whose initial CA-125 value came back elevated.

- Dr. Jonathan Herman, MD