CA-125 (Cancer Antigen 125) is a protein biomarker primarily associated with ovarian cancer. It is commonly used for monitoring disease progression, response to treatment, and detecting recurrence in patients with ovarian cancer. Although elevated CA-125 levels are strongly linked to ovarian malignancies, they can also be seen in benign conditions such as endometriosis, pelvic inflammatory disease, and even during menstruation or pregnancy. While it is not a definitive diagnostic tool due to its lack of specificity, CA-125 is valuable when used in conjunction with imaging and other diagnostic tests.