CA-125 is used to monitor therapy during treatment for ovarian cancer. CA-125 is also used to detect whether cancer has come back after treatment is complete. This test is sometimes used to follow high-risk women who have a family history of ovarian cancer but who do not yet have the disease.

Before a patient starts treatment for ovarian cancer, the doctor will measure a baseline CA-125 to compare against future measurements. During therapy, doctors use CA-125 testing, at intervals, to monitor the response to therapy. CA-125 may also be measured periodically after therapy is completed to catch any early signs of the cancer’s return.

If CA-125 levels fall during therapy, this generally indicates that the cancer is responding to treatment. If CA-125 levels rise, the cancer may not be responding to treatment. High CA-125 levels after treatment is complete may indicate that the cancer has come back.

Because CA-125 can be high in many normal or benign conditions (for example, pregnancy, menstruation, endometriosis, pelvic inflammatory disease) it is not useful as a screening test for cancer.