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Ovarian Cancer Health Center

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Cancer Antigen 125 (CA-125)

Cancer antigen 125 (CA-125) is a protein found on the surface of many ovarian cancer cells. It also can be found in other cancers and in small amounts in normal tissue. A CA-125 test measures the amount of this protein in the blood.

CA-125 is used as a tumor marker, which means the test can help show if some types of cancer are present. Most often, the CA-125 test is used to check how well treatment for ovarian cancer is working or to see if ovarian cancer has returned.

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 developing ovarian cancer. Women have a high risk of getting ovarian cancer if they have a family history of ovarian cancer or certain changes (mutations) in their DNA (BRCA1 or BRCA2).

How To Prepare

You do not need to do anything before you have this test.

How It Is Done

The health professional drawing blood will:

  • Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
  • Clean the needle site with alcohol.
  • Put the needle into the vein. More than one needle stick may be needed.
  • Attach a tube to the needle to fill it with blood.
  • Remove the band from your arm when enough blood is collected.
  • Put a gauze pad or cotton ball over the needle site as the needle is removed.
  • Put pressure to the site and then put on a bandage.
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WebMD Medical Reference from Healthwise

Last Updated: November 14, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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