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Cancer Antigen 125 (CA-125)

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

Cancer Antigen 125 (CA-125) is a protein biomarker primarily used to monitor the progression of certain cancers, particularly ovarian cancer.

Quick summary

CA-125 is a protein biomarker used to monitor cancer progression, especially in ovarian cancer.

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, Fujirebio CA-125
interpretation: {"text":"0–35 U/mL: CA-125 levels within this range are generally considered normal.","label":"Normal"}; {"text":">35 U/mL: Elevated levels 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 in some normal tissues. It is the most widely used biomarker for monitoring ovarian cancer treatment and detecting recurrence.

Elevated levels of CA-125 in the blood can indicate the presence of ovarian cancer or other conditions such as endometriosis, uterine fibroids, or pelvic inflammatory disease. However, it is not specific enough to be used alone for diagnosis.

Regular monitoring of CA-125 levels can help in assessing the effectiveness of cancer treatment and in detecting disease recurrence. A significant increase in CA-125 levels may prompt further diagnostic investigations.

Frequently asked questions

What is the normal range for CA-125 levels?
The normal range for CA-125 levels is typically between 0–35 U/mL.
Can CA-125 levels be elevated in conditions other than cancer?
Yes, conditions such as endometriosis, uterine fibroids, and pelvic inflammatory disease can also cause elevated CA-125 levels.
  1. 1
    American Cancer Society: Ovarian Cancer Early Detection, Diagnosis, and StagingSource
  2. 2
    National Cancer Institute: Cancer BiomarkersSource

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

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

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