CA-125
CA-125 (cancer antigen 125) is a large mucin-like protein made by the MUC16 gene. It sits on certain body-cavity and reproductive-tract surfaces. It sheds into your blood when those surfaces are disrupted. Clinically, a serum CA-125 above 35 U/mL is used as a tumor marker for epithelial ovarian cancer. It mainly tracks treatment response and catches recurrence. But it is weak for early-stage disease, with sensitivity only around 50%. It is also non-specific. Endometriosis, fibroids, pelvic inflammatory disease, fluid around the lungs, and liver cirrhosis can all push it up without cancer. To improve accuracy, the ROMA algorithm (Risk of Ovarian Malignancy Algorithm) combines CA-125 with another marker, HE4. ROMA is preferred over CA-125 alone for sizing up risk before surgery.
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