Summary
CA-125 is a protein that is often raised in ovarian cancer. It is used to help investigate symptoms suggestive of ovarian cancer, to assess pelvic masses alongside imaging, and to monitor response to treatment and detect recurrence. Many benign conditions — including menstruation, endometriosis, and fibroids — also raise CA-125, so results are always interpreted with care.
CA-125 is most useful in women with symptoms or findings suggestive of ovarian cancer. In the UK, NICE recommends measuring CA-125 in women with persistent symptoms such as bloating, abdominal pain, feeling full quickly, or urinary urgency, particularly over the age of 50.
A raised CA-125 prompts further assessment, usually with ultrasound, and a risk score may be calculated. However, CA-125 is not specific: it rises in many benign conditions, especially in premenopausal women (menstruation, endometriosis, fibroids, pelvic infection, pregnancy), and is normal in some ovarian cancers. It is therefore not used for screening healthy women.
In women with diagnosed ovarian cancer, CA-125 is valuable for monitoring — falling levels indicate response to treatment, and rising levels can signal recurrence.
What It Is
CA-125 (cancer antigen 125, MUC16) is a high-molecular-weight glycoprotein expressed by coelomic epithelium-derived tissues, including the ovarian surface and the peritoneum. It is shed into the blood when these tissues are inflamed, irritated, or involved by tumour.
Because CA-125 reflects peritoneal and epithelial irritation in general, it is elevated in many conditions beyond ovarian cancer — limiting its specificity, particularly in premenopausal women. NICE recommends its use to investigate symptomatic women and, with ultrasound and menopausal status, to calculate a risk of malignancy index.
Reference range: approximately < 35 U/mL, varying by laboratory. Levels are interpreted alongside symptoms, imaging, and menopausal status, and serial measurements guide monitoring of known disease.
Functions
Ovarian cancer investigation
Used to investigate symptoms and pelvic masses suggestive of ovarian cancer, alongside imaging.
Treatment monitoring
Tracks response to treatment in ovarian cancer — falling levels indicate response.
Recurrence detection
A rising CA-125 after treatment can signal recurrence, often before symptoms or imaging changes.
Risk assessment
Combined with ultrasound and menopausal status to estimate the risk that a pelvic mass is malignant.
Reference Ranges
CA-125
Measured in U/mL| Status | Range (U/mL) | Range (kU/L) | What it means |
|---|---|---|---|
| Normal | < 35 | Within normal range — though this does not exclude ovarian cancer. | |
| Mildly raised | 35–200 | Mild elevation — often benign, especially in premenopausal women; assess with imaging. | |
| Elevated | > 200 | Significantly raised — increases concern for ovarian cancer; prompt specialist assessment. |
CA-125 is not a screening test. It is commonly raised by benign conditions, particularly in premenopausal women, and can be normal in some ovarian cancers. Interpret with symptoms, imaging, and menopausal status.
Symptoms of Imbalance
CA-125 is measured when ovarian cancer is suspected from symptoms; the marker itself causes none.
- A normal CA-125 is reassuring but does not exclude ovarian cancer
- No symptoms from a low CA-125
- Persistent bloating
- Abdominal or pelvic pain
- Feeling full quickly or loss of appetite
- Urinary urgency or frequency
- Change in bowel habit
- Often no symptoms in early disease
Causes of Imbalance
- Normal in healthy women
- Effective treatment of ovarian cancer (falling CA-125)
- Ovarian cancer
- Endometriosis
- Uterine fibroids
- Menstruation
- Pelvic inflammatory disease
- Pregnancy
- Benign ovarian cysts, liver disease, and other peritoneal irritation
FAQs
Not on its own. CA-125 is often raised in ovarian cancer, but many benign conditions also raise it — including menstruation, endometriosis, fibroids, pelvic infection, and pregnancy — particularly in premenopausal women. A raised CA-125 indicates the need for further assessment, usually with an ultrasound scan and specialist review, rather than confirming a diagnosis of cancer.
No. CA-125 is not used to screen women without symptoms, because it is not specific or sensitive enough: it misses some ovarian cancers and is frequently raised by benign conditions, leading to unnecessary worry and investigation. Its established roles are investigating women with relevant symptoms, helping assess pelvic masses, and monitoring women already diagnosed with ovarian cancer.
In premenopausal women, CA-125 is commonly raised by normal and benign processes — menstruation, endometriosis, fibroids, ovarian cysts, and pelvic inflammation all irritate the tissues that release it. This makes a raised result harder to interpret. CA-125 is more reliable in postmenopausal women, in whom these benign causes are less common, which is reflected in how risk scores are calculated.
In a woman diagnosed with ovarian cancer, CA-125 is measured before and during treatment. A falling level indicates the cancer is responding, while a rising level after treatment can be an early sign of recurrence — sometimes before symptoms or scan changes appear. Serial measurements over time are therefore a valuable part of follow-up care.
References
- NICE. Ovarian cancer: recognition and initial management. CG122. 2011 (updated). View source
- Jacobs I, Bast RC. The CA 125 tumour-associated antigen: a review of the literature. Hum Reprod. 1989;4(1):1–12. View source
- Buys SS, et al. Effect of screening on ovarian cancer mortality: the PLCO randomized controlled trial. JAMA. 2011;305(22):2295–2303. View source