CA 125
Definition
Measures the amount of a protein called CA-125 (cancer antigen 125) in the blood. This protein is a tumor marker produced by cancer cells or by normal cells responding to cancer.
Purpose
- Monitoring treatment effectiveness in patients with diagnosed ovarian cancer
- Detecting recurrence after treatment
- Evaluating suspicious pelvic masses together with imaging
- Screening in high-risk individuals with a strong family history
Results
- A level that falls during treatment → the treatment is working
- A level that rises after treatment → there may be a recurrence
- High risk + high level → additional diagnostic tests are needed
Critical warning: A normal CA-125 result does not rule out ovarian cancer; the level may be low in early-stage cancer.
Normal Values
Laboratory-specific; refer to the reference range on your report.
Risks and Limitations
It cannot be used for screening in people at average risk. Many non-cancerous conditions raise CA-125: endometriosis, pelvic inflammatory disease, uterine fibroids, liver disease, menstruation and pregnancy.