CA-125 blood test (ovarian cancer)

This test measures the amount of a protein called CA-125 (cancer antigen 125) in a sample of your blood. CA-125 is a type of tumor marker. High levels of certain tumor markers in your blood can be a sign of cancer. If you have cancer, measuring certain tumor markers can help provide important information about how to treat your condition.

High levels of CA-125 are often found in people with ovarian cancer. The ovaries are a pair of female reproductive glands that store eggs and produce female hormones. Ovarian cancer occurs when cells in an ovary start to grow uncontrollably.

If you have ovarian cancer, CA-125 blood tests can help show if your treatment is working.

Other names: cancer antigen 125, glycoprotein antigen, ovarian cancer antigen, tumor marker CA-125

A CA-125 blood test may be used:

• To see if the treatment for ovarian cancer is working and to see if the ovarian cancer has come back. This is the most common use of the CA-125 blood test.
• Learn more about a growth or mass in your pelvis (the area under your belly). If a suspicious mass appears during an imaging, such as an ultrasound, your health care provider may check your CA-125 levels along with other tests to determine if the mass could be ovarian cancer. But a CA-125 blood test alone cannot diagnose cancer.
• To screen for ovarian cancer if your risk is very high If your family history includes ovarian cancer, your provider may suggest a CA-125 blood test and other tests to look for signs of cancer. But a CA-125 test is not steps used as a routine screening test for people who do not have a high risk of ovarian cancer. This is because many common conditions that are not cancers can also cause high levels of CA-125, such as endometriosis or even a menstrual period.

If you have been diagnosed with ovarian cancer, you may have multiple CA-125 blood tests:

• During your treatment to see if your cancer goes away. If CA-125 levels fall, it usually means that your treatment is working
• After your treatment, to see if your cancer has come back

If you have a mass in your pelvis that could be ovarian cancer, you may need a CA-125 test to help determine if it could be ovarian cancer. But only a biopsy can diagnose ovarian cancer.

If you have a very high risk of developing ovarian cancer, your health care provider may suggest checking your CA-125 levels. If they are high, you will probably need more tests to find out if you have cancer. You are more likely to develop ovarian cancer if you:

• Do you have a mother or sister, or two or more other family members who have had ovarian cancer
• Do you have family members who have had breast cancer or colorectal cancer (colon cancer)
• Have inherited certain genetic changes or conditions that increase your risk of ovarian cancer, such as:
  • Changes in your genes, including the BRCA 1 or BRCA 2 genes
  • Lynch syndrome (also called hereditary non-polyposis colorectal cancer), an inherited disorder that increases the risk of many types of cancer
• Have had breast, uterine (uterine), or colorectal cancer

If you are concerned about the risk of developing ovarian cancer, talk to your health care provider.

You do not need special preparations for a CA-125 blood test.

There is very little risk in taking a blood test. You may experience mild pain or bruising where the needle was inserted, but most symptoms go away quickly.

Your provider will review your CA-125 test results along with other information about your condition. Together, you can discuss how your results affect your diagnosis, treatment, and the need for additional testing.

In general:

• If you are being treated for ovarian cancer, and if the results of several tests show that your CA-125 levels are decreasing, that usually means that the treatment is working. If your levels increase or stay the same over time, it may mean that the treatment is not working.
• If you have finished your treatment for ovarian cancer and as your CA-125 levels start to rise over time, your cancer could come back.
• If you have a high risk of ovarian cancer or if you have a suspicious pelvic mass, a high CA-125 level could be a sign of cancer. Your provider will usually order additional tests to make a diagnosis.

A high CA-125 level does not always mean cancer. Other conditions may increase CA-125, including:

• Endometriosis
• Pelvic Inflammatory Disease (PID)
• Uterine fibroids
• Liver disease
• Pregnancy
• Your menstrual period, at certain points in your cycle

A normal CA-125 test result does not rule out ovarian cancer. This is because CA-125 levels may be low in the early stages of cancer. And not everyone with ovarian cancer produces high levels of CA-125.

Talk to your provider if you have questions about your results.

Learn more about lab tests, reference ranges, and understanding results.

The most common type of ovarian cancer is epithelial ovarian cancer. If you have been treated for this type of cancer, you may be tested for a tumor marker called HE4 in addition to CA-125. Some studies show that measuring both tumor markers provides more accurate information to check if the treatment is working and to look for the return of this type of cancer.

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