Testing for levels of cancer antigen 125, or CA-125, is not considered accurate enough to be used as a method of screening women for ovarian cancer, according to Mayo Clinic. However, it is useful in monitoring patients during treatment or identifying women at high risk of ovarian cancer.
CA-125 levels are not higher than normal in many women with early-stage ovarian cancer, and thus CA-125 tests are not used to screen for this disease, according to the Canadian Cancer Society. More advanced ovarian cancers can cause an increase in CA-125 levels; however, many other cancers can increase CA-125 levels as well. A reduction in the CA-125 level in an ovarian cancer patient who is undergoing treatment can be indicative of effective treatment.