CA-125
Reviewed by Maurice Lichtenberg
CA-125 (cancer antigen 125) is a high-molecular-weight mucin-like glycoprotein encoded by MUC16 and expressed on coelomic and Müllerian-derived epithelium; it is shed into the circulation in proportion to epithelial surface disruption. Serum CA-125 above 35 U/mL is used clinically as a tumour marker for epithelial ovarian cancer, particularly for monitoring response to treatment and detecting recurrence, though sensitivity for early-stage disease is limited to approximately 50%. Elevated CA-125 is non-specific: endometriosis, uterine fibroids, pelvic inflammatory disease, pleural effusion, and hepatic cirrhosis can all produce substantial elevations in the absence of malignancy. The multivariate Risk of Ovarian Malignancy Algorithm (ROMA), combining CA-125 with HE4, improves diagnostic specificity and is preferred over CA-125 alone for pre-operative risk stratification.