What Is the Cancer Antigen 27.29 Test?

Tumor Marker Test That Monitors Metastatic Breast Cancer

Sometimes blood tests that check for proteins called antigens can be used to help monitor cancer treatment response or to detect a recurrence. While these tests are not the only tools that should be used to monitor your cancer, they are helpful.

One of these tests is the cancer antigen 27.29 (CA 27.29) blood test. This is used to check for an antigen associated with breast cancer. An antigen is a protein on the surface of a cell that serves as an identifier. And CA 27.29 is one of several antigens that healthcare providers use as tumor markers for breast cancer.

The CA 27.29 test is primarily used to monitor stage 4 metastatic breast cancer and less commonly to detect recurrence in people previously treated for early-stage breast cancer. A higher antigen level corresponds to recurrence, and a lower antigen level corresponds to treatment response.

Although the CA 27.29 test was approved by the Food and Drug Administration (FDA) to help monitor people with breast cancer, the antigen can be detected with other cancerous and noncancerous conditions.

What to Know About the CA 27.29 Antigen Test

Theresa Chiechi / Verywell

Purpose of Test

Tumor markers are substances made either by the body in response to cancer or by the tumor itself. Found in blood, urine, and tissue samples, these markers are signals of specific disease processes. This can help healthcare providers distinguish between the types and/or stages of cancer.

Although CA 27.29 is commonly associated with breast cancer, it may also be found in colon, stomach, liver, lung, pancreatic, ovarian, and prostate cancers. While some tumor marker tests are useful for screening or staging cancer, the CA 27.29 test is limited to the following two functions:

  • Monitoring progression of metastatic breast cancer, with increasing values corresponding to advancing disease
  • Monitoring treatment of metastatic breast cancer, with lowering values corresponding to a positive treatment response

CA 27.29 levels will most likely rise during the first 30–90 days of cancer treatment for some patients. This is because treatment can cause the tumor to release CA 27.29 antigens into the bloodstream. Because of this, your oncologist may wait two to three months after the start of each new treatment to get an accurate test result.

Although tumor marker tests like the CA 27.29 can aid in the management of breast cancer, they can't definitively diagnose the disease. Only a breast biopsy can diagnose breast cancer.


Studies have shown that the test results don't specifically differentiate breast cancer from other causes, including noncancerous causes.

There is currently no evidence showing subsequent improvements in survival or quality of life as a result of this test, according to a 2014 study in the Journal of Cancer.

A 2017 article in the Journal of Oncological Sciences states that because its sensitivity is low and it can't always specify what it is detecting, it is a better tool for monitoring disease progression and detecting metastases (areas cancer has spread to). It should not be used for diagnosing breast cancer or screening for the disease.

As of November 2007, the American Society of Clinical Oncologists (ASCO) has advised against the use of the tumor marker tests to monitor for recurrence in people with no signs or symptoms of breast cancer.

Routine mammography is the preferred method of breast cancer screening, whether for new or recurring disease.


The CA 27.29 is a blood-based test requiring one full test tube of blood, which is collected with a blood draw. As such, the risks of the test are relatively small. Injection site pain, bruising, or bleeding are possible, as is light-headedness or fainting. Infection is rare, but can occur.

Before the Test

It is rare that the CA 27.29 is ordered on its own. Your oncologist will more than likely order a battery of tests to monitor your cancer or its response to therapy. This may include a complete blood count (CBC), liver functions tests, and kidney function tests. No preparation is needed for any of these tests.


The blood draw only takes a few minutes to perform. Depending on registration and waiting time, expect to spend between 30 to 90 minutes at the testing site.


If your oncologist recommends a CA 27.29 test, the blood draw can often be done in the healthcare provider's office during your visit. You may also be referred to a nearby lab.

What to Wear

When going to your test, wear a top that is either short-sleeved or has sleeves that can easily be rolled up. Some people prefer wearing long sleeves so that they can cover the bandage or puncture mark after the test.

Food and Drink

There are no food or drink restrictions for the CA 27.29 test.


You should tell the phlebotomist (the medical professional drawing blood) if you are taking Herceptin (trastuzumab) or any other monoclonal antibodies derived from mouse antigens because they can affect your results. If you are unsure whether a drug you're taking might alter your CA 27.29 test, speak with your oncologist.

Cost and Health Insurance

The cost of a CA 27.29 test can vary by location and lab, and it generally runs about $70. Your health insurance will usually cover some or all the cost if you have metastatic breast cancer. This may not be true if the test is used for screening purposes.

Speak with your insurance company to confirm what your co-pay or coinsurance costs will be in advance of the test. You should also check that the lab used is an in-network provider, or you may find yourself having to pay the full price.

If you don't have insurance and must pay out of pocket, you can shop around for the best price. You should also ask your oncologist for information regarding financial assistance programs that can help pay for your ongoing treatment and care.

What to Bring

Be sure to bring a method of identification, your health insurance card, and a form of payment to cover any copay, coinsurance, or out-of-pocket costs.

During the Test

When you arrive for the test, you will need to check in, complete a registration form, and make payment for any out-of-pocket costs. A consent form may be provided.

A phlebotomist will perform the blood draw.


You will be led to a room and seated in a chair. The phlebotomist will ask which arm you prefer the blood drawn from. Some people suggest the arm you don't write with; others recommend the arm with the most prominent veins.

After placing an elastic tourniquet around your upper arm, the phlebotomist will swab the puncture site (typically the crook of the arm) with an alcohol swab.

Throughout the Test

You will feel a tiny prick as the needle is inserted into your vein.

For the CA 27.29 test, a full test tube of blood (minimum of 3 milliliters) is needed. The vacuum-sealed tube will usually have a gold or red rubber cap.

Once completed, the needle will be withdrawn and a cotton ball or gauze will be placed on the puncture site until the bleeding stops (usually within a minute). The phlebotomist will then put an adhesive bandage over the wound.


You should be able to leave shortly after your test is completed as long as you are not bleeding or feeling dizzy. After that, you can continue with your day without limitations.

After the Test

After the test, it is not uncommon to feel mild soreness at the puncture site for the first couple of hours. Redness or bruising may also occur. Once the bleeding is fully stopped, you can remove the adhesive bandage. However, if the puncture wound is visible, you need to keep it covered to prevent infection.

Although infection is rare, it can sometimes occur. Call your healthcare provider if you experience continuing or worsening pain in your arm or hand, develop a high fever, or have persistent bleeding after the blood draw.

Interpreting Results

The results of your blood test should be available within three to five working days. The report will include a reference range, outlining levels of the CA 27.29 antigen that are considered normal or abnormal. The reference range is based on the expected values in a population of people.

While the CA 27.29 reference range can vary slightly from one lab to the next, it is generally accepted that anything less than 38.6 units per millimeter (U/mL) is normal. A normal result generally indicates that you don't have an active cancer.

A CA 27-29 value higher than 38.6 U/mL can indicate one of the following:

  • You have active cancer.
  • Cancer may be spreading.
  • Cancer may be recurring.
  • You have another cancerous or noncancerous condition.
  • You have been exposed to mouse-derived antibodies.

Generally speaking, cancer is suggested when the CA 27.29 value is over 100 U/mL. An increase of more than 25% between tests is also considered clinically significant.

If the CA 27.29 test is used to monitor your response to treatment, a single value is less important than how the results trend over time. Decreasing values are an indication that a treatment is working, while increasing or stagnating values may suggest that treatment is not working.

False Positives

Aside from the recent start of cancer treatment, there are other things that pose a risk of a false-positive result. A sudden rise in CA 27.29 levels may occur for reasons other than breast cancer, be them benign or cancerous.

Such conditions include:


If your CA 27.29 results are abnormally elevated, your oncologist will likely order additional tests to determine the cause.

These may include:


The CA 27.29 blood test can help your doctor monitor your cancer and its response to treatment. Taken together with other tools and clinical monitoring, this is a helpful test to have. It is mostly noninvasive with minimal pain and adds to the larger clinical picture. While it is not helpful for diagnosis or staging, it can be used in other ways.

A Word From Verywell

The CA 27.29 test is an important tool for monitoring the treatment and care of metastatic breast cancer. The test can be used to monitor your response to treatment and/or assess whether cancer is active or spreading, but it has its limitations. Even if a value is high, you should not assume that cancer is the cause. The CA 27.29 is only useful when used in combination with other tests.

If you are worried about your results or have concerns about your CA 27.29 numbers, talk with your doctor. Cancer is not the only thing that can increase this tumor marker, and your doctor is using this test as part of the bigger picture.

Frequently Asked Questions

  • What is a cancer antigen number?

    A cancer antigen number is also called a tumor marker. It is a number that indicates the amount of cancer antigen in the body. A cancer antigen is a protein made by cancer cells. Different types of cancer can make different types of antigens.

  • What does a high CA 27.29 mean?

    A high CA 27.29 marker can mean a variety of things. Yes, it can signify that your cancer is not responding to treatment or that it has metastasized, but there are also reasons not related to cancer for why the number could be high. Your doctor will be able to review your results and order any other tests to further evaluate the underlying reasons for the high number.

  • Can stress cause tumor markers to rise?

    There is no clear link between stress and cancer or rising tumor markers. One study found that in mice, stress hormones can trigger an immune cell reaction that reawakened inactive (dormant) cancer cells. However, that does not mean stress will trigger a recurrence.

  • Can tumor markers rise during chemo?

    Yes, they can—and this is normal. Especially in the beginning of chemotherapy, as the treatment breaks down the cancer, it can release the antigen, causing an increase in the tumor marker. The test should be redone three to four months after being on any new treatment in order to get a more accurate result.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  6. American Society of Clinical Oncologists. American Society of Clinical Oncology 2007 Update of Recommendations for the Use of Tumor Markers in Breast Cancer. J Oncol Pract. 2007 Nov;3(6):336-9. doi:10.1200/JOP.0768504.

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Additional Reading
Originally written by Pam Stephan
Pam Stephan is a breast cancer survivor.
Learn about our editorial process