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CA-125

Also known as: CA 125 tumor marker
Formal name: Cancer Antigen 125
Related tests: Tumor markers, BRCA-1 and BRCA-2

At a Glance

Why Get Tested?

To monitor treatment for ovarian cancer or to detect recurrence

When to Get Tested?

Before starting therapy for ovarian cancer or if at high risk for developing ovarian cancer, and at intervals during and after treatment

Sample Required?

A blood sample drawn from a vein in the arm

The Test Sample

What is being tested?

The Cancer Antigen 125 (CA-125) test measures the amount of CA-125 in the blood. CA-125 is a protein that is present on the surface of most, but not all, ovarian cancer cells. Significantly elevated concentrations of CA-125 may be present in the blood of a woman who has ovarian cancer. 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.

The Test

How is it used?

CA-125 is primarily used to monitor therapy during treatment for ovarian cancer. CA-125 is also used to detect whether cancer has come back after treatment is complete. Series of CA-125 tests that show rising or falling concentrations are often more useful than a single result. This test is sometimes used to test and monitor high-risk women who have a family history of ovarian cancer but who do not yet have the disease.

This test is not used to screen for ovarian cancer because it is non-specific. Levels in the blood can be elevated in other conditions such as normal menstruation, pregnancy, endometriosis, and pelvic inflammatory disease.

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When is it ordered?

A doctor may order a CA-125 test before a woman starts ovarian cancer treatment as a baseline to compare against future measurements. During therapy, physicians order CA-125 testing at intervals to monitor response to therapy. CA-125 may also be measured periodically after therapy is completed. An increase in CA-125 may indicate that the cancer has returned.

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What does the test result mean?

If CA-125 levels fall during therapy, this generally indicates that the cancer is responding to treatment. If CA-125 levels rise or stay the same, then the cancer may not be responding to therapy. High CA-125 levels after treatment is complete may indicate that the cancer has come back.

If a woman who has been diagnosed with ovarian cancer has a baseline CA-125 level that is normal, then the test is not likely to be useful to monitor her ovarian cancer. In this case, the ovarian cancer may not be producing CA-125 so it is not a good marker of disease progression.

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Is there anything else I should know?

Because CA-125 can be high in many normal or benign conditions, such as pregnancy, menstruation, endometriosis, and pelvic inflammatory disease, it is not useful or recommended as a screening test for the general population.

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Common Questions

1.  Is CA-125 always increased in ovarian cancer?

No, not all ovarian cancers are associated with increased levels of CA-125. Elevated levels have been found in about 80% of women with ovarian cancer.

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2.  My CA-125 is elevated. Does that mean I have cancer?

No. CA-125 may be elevated in several other conditions and diseases. This means it is not specific for ovarian cancer. CA-125 may normally be increased in early pregnancy and during menstruation. It can also be increased in diseases such as pelvic inflammatory disease or endometriosis and sometimes in hepatitis and cirrhosis of the liver.

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3.  Does ovarian cancer run in families?

Family history is a risk factor for ovarian cancer. If you have close family members who have had ovarian cancer, you are at higher risk than someone who has no family history of the disease. Make sure your doctor knows about your family medical history.

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4.  What are some other risk factors for ovarian cancer?

In addition to family history, other risk factors include increasing age, obesity, and use of hormone replacement therapy. See the American Cancer Society web site for more on this.

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

Pagana, K. D. & Pagana, T. J. (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 219-220.

Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 210-211.

Mason, J. (Updated 2008 June 10). CA-125. MedlinePlus Medical Encyclopedia. [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/007217.htm. Accessed March 2009.

(2007 March). Ovarian Cancer Resource Guide for women with recurrent disease. NOCC, Inc. [On-line information]. PDF available for download at http://www.ovarian.org/Images/ResourceGuideRecurrentOvarianCancer.pdf through http://www.ovarian.org. Accessed March 2009.

(2008 August 26). Ovarian Cancer: Why Screening Isn't Routine. American Cancer Society. [On-line information]. Available online at http://www.cancer.org/docroot/SPC/content/SPC_1_ovarian_Q_A_Saslow.asp through http://www.cancer.org. Accessed March 2009.

(Modified 2008 April 3). Ovarian Cancer Screening (PDQ®), Health Professional Version. NCI, U.S. National Institutes of Health. [On-line information]. Available online at http://www.cancer.gov/cancertopics/pdq/screening/ovarian/healthprofessional through http://www.cancer.gov. Accessed March 2009.

(2008 July). Understanding CA 125 Levels: A Guide for Ovarian Cancer Patients. Gynecologic Cancer Foundation. [On-line information]. PDF available for download at http://www.thegcf.org/wcnlib/downloads/CA125levels_July2008.pdf through http://www.thegcf.org. Accessed March 2009.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.