This assay is useful for evaluating patient's response to ovarian cancer therapy. It also helps in predicting recurrent ovarian cancer or intraperitoneal tumor, especially for ovarian carcinoma Predicting recurrent ovarian cancer or intraperitoneal tumor. Elevated CA 125 levels are seen in many patients with cancer of the ovary. The percentage of positive cases increases with stage of the cancer. Cancer Antigen 125 (CA-125) is a tumor marker primarily 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. A series of CA-125 tests that shows rising or falling concentrations is often more useful than a single result.