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[Biochemistry](https://durgical.com/en/biochemistry/) · Topic

# CA-125

CA-125 is a mucin of coelomic linings; it follows epithelial ovarian cancer but rises in many benign conditions.

Updated 2026-11-01

## Key facts

- A mucin-type glycoprotein (MUC16) of coelom-derived linings: peritoneum, pleura, pericardium, endometrium, fallopian tubes.
- Main use: follow-up of epithelial (serous) ovarian cancer during and after treatment.
- It is not useful to screen women without high risk: it is normal in many early-stage cancers.
- It rises in endometriosis, menstruation, pregnancy, pelvic inflammatory disease, fibroids, cirrhosis with ascites, pleural effusion and heart failure.
- It is more useful after menopause, when there are fewer benign causes; its reference value varies by laboratory.

## In detail

- What it measures: CA-125 antigen in serum by immunoassay.
- Where it comes from: mesothelial and Müllerian cells express it on their surface; any serosal irritation or epithelial tumour releases it.
- Why it rises: epithelial ovarian cancer, other cancers (endometrium, tube, pancreas, lung), peritoneal or pleural irritation of any cause.
- Pitfalls: false positives are common before menopause; any ascites raises it.
- It is combined with ultrasound and menopausal status in risk-of-malignancy indices to decide referral of an adnexal mass.

**Also called**
Cancer antigen 125, MUC16

## Clinical notes

- A complex adnexal mass with a high CA-125 in a postmenopausal woman is referred to gynaecological oncology.
- A CA-125 rising again after chemotherapy may herald relapse before symptoms.
- In women with BRCA mutations it has been used with ultrasound for surveillance, with limited benefit.

## Related conditions

- [Ovarian cancer](https://durgical.com/en/conditions/ovarian-cancer/)
- [Endometriosis](https://durgical.com/en/conditions/endometriosis/)
- [Pelvic inflammatory disease](https://durgical.com/en/conditions/pelvic-inflammatory-disease/)
- [Cirrhosis](https://durgical.com/en/conditions/cirrhosis/)
- [Uterine fibroids (leiomyomas)](https://durgical.com/en/conditions/uterine-fibroids/)

## Related

- [Tumour markers: principles of use](https://durgical.com/en/biochemistry/topics/tumour-markers-principles-of-use/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which cancer is followed with CA-125?

Epithelial ovarian cancer, especially the serous type.

## Why is CA-125 more useful after menopause?

Before menopause many benign causes raise it (endometriosis, menstruation, fibroids, pregnancy).

## What do the benign causes of a high CA-125 have in common?

They irritate coelomic linings (peritoneum, pleura, pericardium) or the endometrium, which express this mucin.

## Is CA-125 useful to screen for ovarian cancer in women without high risk?

No; it is normal in many early tumours and gives frequent false positives.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [CA-125 Blood Test (Ovarian Cancer): MedlinePlus Medical Test](https://medlineplus.gov/lab-tests/ca-125-blood-test-ovarian-cancer/) (MedlinePlus, US National Library of Medicine, 2026); [CA-125 blood test: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/007217.htm) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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