CA-125
Also called: CA 125, Cancer antigen 125, MUC16
Cancer antigen 125 — best known as a marker for ovarian cancer follow-up. Has many benign causes of elevation and is NOT a screening test in average-risk women.
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What does CA-125 measure?
CA-125 is a mucin-family glycoprotein (also called MUC16) shed by ovarian epithelial cells and many other tissues. It's most established for monitoring known epithelial ovarian cancer — tracking response to chemotherapy and detecting recurrence after surgery. As a screening test in average-risk women it performs poorly: too many false positives (endometriosis, fibroids, menstruation, pregnancy, pelvic inflammatory disease, cirrhosis, heart failure) and false negatives (early-stage and mucinous tumours often miss). The American Cancer Society, USPSTF and other major bodies recommend AGAINST CA-125 screening in average-risk women.
What does a high CA-125 level mean?
- Ovarian, fallopian-tube and primary peritoneal cancer — the established indications.
- Benign gynaecological conditions — endometriosis, uterine fibroids, ovarian cysts, pelvic inflammatory disease.
- Menstruation, pregnancy, recent pelvic surgery — physiological / iatrogenic.
- Other cancers — lung, breast, pancreas, colon (less specific).
- Cirrhosis, heart failure, peritonitis — non-specific elevations.
What does a low CA-125 level mean?
- Low or normal CA-125 does NOT rule out ovarian cancer in a symptomatic woman; complementary imaging and clinical work-up are needed.
When to discuss with a doctor
If you have CA-125 ordered in the context of a known ovarian cancer or with concerning gynaecological symptoms (persistent bloating, abdominal pain, early satiety), the result belongs in conversation with your gynaecologist or oncologist. An incidentally elevated CA-125 in a woman without symptoms is far more likely to reflect a benign cause; Mediora.AI shows the value with the benign-vs-malignant context but cannot make this call alone.