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CA-125

Formal name: Cancer antigen 125
Related tests: Tumour markers, BRCA-1 and BRCA-2

At a Glance

Why Get Tested?

To monitor treatment for ovarian cancer

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

Test Preparation Needed?

None

The Test Sample

What is being tested?

CA-125 is a protein often found on the surface of ovarian cancer cells and in some normal tissues. It is used as a marker for ovarian cancer. However, CA-125 levels may also be high in other types of non-cancerous conditions, including menstruation, pregnancy, and pelvic inflammatory disease.

How is the sample collected for testing?

Blood is drawn from a vein in the arm.

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 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. This test is sometimes used to follow high-risk women who have a family history of ovarian cancer but who do not yet have the disease.

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When is it requested?

Before a patient starts treatment for ovarian cancer, the doctor will measure a baseline CA-125 to compare against future measurements. During therapy, doctors use CA-125 testing, at intervals, to monitor the response to therapy. CA-125 may also be measured periodically after therapy is completed to catch any early signs of the cancer’s return.

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What does the test result mean?

Looking for reference ranges?

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

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Is there anything else I should know?

Because CA-125 can be high in many normal or benign conditions (for example, pregnancy, menstruation, endometriosis, pelvic inflammatory disease) it is not useful as a screening test for cancer.

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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. 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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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.