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CA 27-29

Does this test have other names?

Cancer antigen 27-29

What is this test?

CA 27-29 is a blood test used to monitor certain types of cancer. CA 27-29 is the name of an antigen, which is a substance that stimulates your body's defense system. Certain types of cancer cells release CA 27-29 antigen into the blood. This test measures the levels of CA 27-29 in your blood.

Breast cancer is the cancer most likely to release CA 27-29, and the FDA has approved the CA 27-29 blood test as a way for doctors to monitor people with breast cancer. Antigens like CA 27-29 that provide information about cancer are called tumor markers. 

Why do I need this test?

CA 27-29 is not a screening test to find out whether you have breast cancer. If you have been diagnosed with breast cancer, your health care provider may order the CA 27-29 test:

  • To find out whether your cancer has spread before starting treatment

  • To find out how well your treatment is working

  • To find out whether your cancer has come back or spread after treatment

What other tests might I have along with this test?

Your doctor may check for another breast cancer tumor marker called CA 15-3. You may also have other diagnostic tests. 

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

It's important to know that a positive CA 27-29 test does not mean you have breast cancer or that breast cancer has come back. Your test results can be higher than normal for other types of cancer, such as liver, pancreatic, ovarian, and colorectal cancers. Some conditions that aren't cancer may cause a positive CA 27-29 test. Notably, some people with breast cancer do not have a positive CA 27-29 blood test. 

Health providers measure CA 27-29 in units per milliliter (U/mL). A normal test should be less than or equal to 38 U/mL. Here is what your test results may mean:

  • If your CA 27-29 is less than 38 U/mL, it may mean that you don't have active breast cancer.

  • If your CA 27-29 is 38 U/mL or greater, you may have active breast cancer, your breast cancer may have come back, or your breast cancer may have spread. When breast cancer spreads to an area outside the breast, it is called metastasis.

  •  If your CA 27-29 is 38 U/mL or greater, you may have a condition other than breast cancer that raises CA 27-29. These conditions include other types of cancers, as well as noncancerous breast diseases, cysts of the ovary, and liver disease. When CA 27-29 goes up because of a condition other than cancer, the test is called a false-positive. 

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Some noncancerous conditions may cause a false-positive CA 27-29. You may also have a false-positive result if you are exposed to mouse antigens in your environment or if you receive cancer treatments that use mouse antigens.

How do I get ready for this test?

You don't need to prepare for this test.