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Cancer Antigen 125 (CA-125)

Published: July 27, 2026Updated: August 25, 2026

CA-125 is a protein biomarker often used to monitor the treatment and progression of ovarian cancer.

Quick summary

CA-125 is primarily used to monitor ovarian cancer treatment and progression.

Medically reviewed by WellAlly Editorial TeamLast reviewed August 25, 2026Editorial policy

Key facts at a glance

Units
U/mL
Clinical utility
monitoring
Result kind
quantitative
FDA-cleared
Roche CA 125, Abbott CA 125, Siemens CA 125, Beckman CA 125
interpretation: {"text":"0–35 U/mL: CA-125 levels within this range are generally considered normal.","label":"Normal"}; {"text":">35 U/mL: Levels above 35 U/mL may indicate the presence of ovarian cancer or other conditions.","label":"Elevated"}

CA-125, or Cancer Antigen 125, is a protein that is often found on the surface of ovarian cancer cells and can be detected in the blood. Elevated levels of CA-125 are commonly associated with ovarian cancer, although they can also be elevated in other conditions such as endometriosis, uterine fibroids, and even during pregnancy.

In the context of oncology, CA-125 is primarily used to monitor the effectiveness of treatment for ovarian cancer and to detect disease recurrence. A decrease in CA-125 levels often indicates a positive response to treatment, while an increase may suggest disease progression or recurrence.

While CA-125 is a valuable tool in managing ovarian cancer, it is not used as a screening test due to its lack of specificity. Other diagnostic tests and clinical assessments are necessary to confirm a diagnosis of ovarian cancer.

Frequently asked questions

What does a high CA-125 level mean?
A high CA-125 level may indicate ovarian cancer, but it can also be elevated in other conditions such as endometriosis, uterine fibroids, and during pregnancy.
Is CA-125 used for screening?
No, CA-125 is not recommended for ovarian cancer screening due to its lack of specificity and the high rate of false positives.
  1. 1
    American Cancer Society: Ovarian Cancer TestsSource
  2. 2
    National Cancer Institute: CA-125Source

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

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Medically reviewed by WellAlly Editorial Team Last reviewed August 25, 2026. · Read our editorial policy