The CA-125 test measures the level of cancer antigen 125 in the blood, a protein often found in higher concentrations on the surface of ovarian cancer cells and some other healthy tissues. It is primarily utilized as a tumor marker to monitor the effectiveness of ovarian cancer treatment and to detect potential disease recurrence. While a valuable tool in management, CA-125 is not a definitive diagnostic test for initial screening, as elevated levels can also be caused by benign conditions such as endometriosis, uterine fibroids, and pelvic inflammatory disease, limiting its specificity.