CA-125 (Cancer Antigen 125), encoded by the MUC16 gene,is a high molecular weight transmembrane glycoproteinbelonging to the mucin family. It is not expressed in normalovarian surface epithelium but is detected in tissues suchas cervix, endometrium, and fallopian tube epithelium.Pathologically, CA-125 shows strong and diffuse expressionin the majority of ovarian serous carcinomas and inepithelioid mesotheliomas, making it an importantresearch marker for gynecologic malignancies. CA-125immunostaining is also widely used in studies of tumorprogression and in validating biomarkers for ovarian cancermodels.