Cancer Antigen 125 (CA-125)

CA-125 (Cancer Antigen) Test, Carbohydrate Antigen (CA-125) Test

Why It Is Done

The test for cancer antigen 125 (CA-125) is used to:

• Check to see if treatment for cancer is working. If the level of CA-125 is going down, it usually means that the treatment is working.
• Check to see if ovarian cancer has returned.
• Check to see if the ovary is the main site of cancer in a woman. If a doctor has found a cancer that has spread to another part of the body (metastatic cancer), he or she may do a CA-125 test to find out where the cancer started. High levels of CA-125 are a strong sign that the cancer started in the ovary. But other types of cancer can increase CA-125 levels too.

The CA-125 test is not recommended as a screening test for ovarian cancer at this time because it often has false-positive results. But the CA-125 test and an ultrasound scan may be used to test women who have a high chance of ovarian cancer. Women have a high risk of ovarian cancer if they have a family history of ovarian cancer or certain changes (mutations) in their DNA (BRCA1 or BRCA2).

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Author:	Bets Davis, MFA	Last Updated: June 9, 2009
Medical Review:	Joy Melnikow, MD, MPH - Family Medicine Douglas A. Stewart, MD - Medical Oncology
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