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CA-125

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Also known as: CA 125 Tumor Marker
Formal name: Cancer Antigen 125

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The Test Sample

What is being tested?

Cancer Antigen 125 (CA-125) is a protein that is present on the surface of most, but not all, ovarian cancer cells. This makes the test useful as a tumor marker in specific circumstances. The CA-125 test measures the amount of CA-125 in the blood.

Significantly elevated concentrations of CA-125 may be present in the blood of a woman who has ovarian cancer. Thus the test may be used to monitor the effectiveness of treatment and/or for recurrence of the cancer. However, not all women with ovarian cancer will have elevated CA-125 so the test may not be useful in all cases.

Ovarian cancer is the fifth most common cause of cancer death in women. According to the American Cancer Society (ACS), the lifetime risk of a woman developing ovarian cancer is about 1 in 75 and the lifetime risk of death is 1 in 100. ACS estimates that about 22,000 new cases are diagnosed each year in the U.S. and about 14,000 women die of it.

Currently, less than 20% of ovarian cancers are found in the early stages before they have spread outside the ovary. The primary reason they go undetected is that the symptoms of ovarian cancer are fairly non-specific.

The need for a reliable method for early detection of ovarian cancer among asymptomatic women continues to drive ongoing research. In the meantime, regular physicals, pelvic exams, and an awareness of family history and symptoms are important.

CA-125 is not recommended as a screening test for asymptomatic women because it is non-specific. Small quantities of CA-125 are produced by normal tissues throughout the body and by some other cancers. Levels in the blood may be moderately elevated with a variety of non-cancerous conditions, including menstruation, pregnancy, and pelvic inflammatory disease.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.