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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 watch certain types of cancer. CA 27-29 is the name of an antigen. An antigen is a substance that stimulates your body's defense system. Certain types of cancer cells send CA 27-29 antigen into the blood. This test measures how much CA 27-29 is in your blood.

Breast cancer is the cancer most likely to release CA 27-29. The FDA has approved the CA 27-29 blood test as a way for healthcare providers to monitor people with breast cancer. Antigens like CA 27-29 that give 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 healthcare 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 healthcare provider 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?

Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you. 

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

Healthcare 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. They also include 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 is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Does this test pose any risks?

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore. 

What might affect my test results?

Some conditions that are not cancer may cause a false-positive CA 27-29. You may also have a false-positive result if you are in contact with mouse antigens in your environment. You may have a false-positive if you get cancer treatments that use mouse antigens.

How do I get ready for this test?

You don't need to prepare for this test. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.  

Medical Reviewers:

  • Greco, Frank MD
  • Sather, Rita, RN