CA-125 (cancer antigen 125) is a protein found on the surface of many ovarian cancer cells and released into the bloodstream. It is the most widely used tumour marker for ovarian cancer, although it is not specific to ovarian cancer and can be elevated in many other conditions including endometriosis, fibroids, pelvic inflammatory disease, and various benign gynaecological conditions.
CA-125 is primarily used to monitor the response to treatment in women with confirmed ovarian cancer, and to detect recurrence after treatment. It is less useful as a standalone screening tool in the general population due to its low specificity — many women with elevated CA-125 do not have ovarian cancer, and approximately 20% of ovarian cancers (particularly early-stage mucinous types) do not produce CA-125. It is most clinically meaningful when used in combination with pelvic ultrasound and clinical assessment.
FAQs
Does an elevated CA-125 mean I have ovarian cancer?
Not necessarily. Many benign conditions elevate CA-125 including endometriosis, fibroids, and pelvic inflammatory disease. An elevated CA-125 requires further investigation with ultrasound and clinical assessment, but it does not diagnose cancer. Conversely, early-stage ovarian cancer often does not elevate CA-125.
Is CA-125 a good screening test for ovarian cancer?
CA-125 is not recommended as a standalone routine screening test in the general population because it has poor specificity — too many false positives from benign conditions. It is most valuable for monitoring known ovarian cancer and assessing suspicious pelvic masses alongside ultrasound.
What CA-125 level is concerning?
Levels above 35 U/mL are considered elevated, but clinical context is essential. In postmenopausal women with a pelvic mass, even modestly elevated CA-125 is more concerning than in premenopausal women where benign causes are more common. Very high levels (above 200–500 U/mL) and rising serial results are more strongly associated with malignancy.
How is CA-125 used after ovarian cancer treatment?
After treatment, CA-125 is measured regularly (every 3–6 months) during surveillance. A persistently normal CA-125 is reassuring. A rising CA-125 — even before symptoms develop — often indicates recurrence and prompts imaging and consideration of further treatment.
