CA 27-29

Does this test have other names?

Cancer antigen 27-29

What is this test?

CA 27-29 is the name of an antigen. An antigen is a substance that stimulates your body's immune 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. Antigens like CA 27-29 that give information about cancer are called tumor markers.

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 health care providers to check people with breast cancer.

Why do you 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.

• How well your treatment is working.

• Whether your cancer has come back or spread after treatment.

What other tests might you have along with this test?

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

What do your test results mean?

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your health care 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. 

Health care 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 your 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 you get ready for this test?

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