What Is the Cancer Antigen 27.29 Test?

Tumor marker test used to monitor metastatic breast cancer

The cancer antigen 27.29 (CA 27.29) test is a blood test used to detect an antigen associated with breast cancer. An antigen is a proteins on the surface of a cell that serves as its unique identifier. CA 27.29 is one of several antigens that healthcare providers use as tumor markers for breast cancer. These markers tend to increase whenever cancer is present.

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.

Although the CA 27.29 test was approved by the U.S. Food and Drug Administration (FDA) to help monitor people with breast cancer, the antigen can occur 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 cancer itself. Found in blood, urine, and tissue samples, these markers are indicative of a specific disease process and can help healthcare providers distinguish between the types and/or stages of cancer.

CA 27.29 is specific to breast cancer but may also be detected in colon, stomach, liver, lung, pancreatic, ovarian, and prostate cancer. 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 almost invariably rise during the first 30 to 90 days of cancer treatment for some patients as the disruption of the tumor releases CA 27.29 antigens into the bloodstream. Because of this, your oncologist may need to 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, neither they or any other blood or imaging test can definitively diagnose the disease. Only a breast biopsy can.


Up until 2007, the CA 27.29 test was used by many to monitor for recurrence in people previously treated for stage 2 or stage 3 breast cancer.

At that time, it was suggested that the test had a predictive value of over 80%, meaning that more than eight in 10 breast cancer recurrences were accurately diagnosed using the test. It was further shown that the test could detect increases up to five months before symptoms developed or imaging tests could identify cancerous growth.

Since that time, numerous studies have shown that the test is far less sensitive than previously thought and that it lacked the specificity to differentiate breast cancer from other benign or malignant causes.

In fact, a 2007 Journal of Clinical Oncology study reported that less than 60% of CA 27.29 tests were able to correctly identify breast cancer even when the malignancy was positively detected on a PET/CT scan.

Even if the test were able to make the identification, there is currently "no evidence showing subsequent improvements in survival or quality of life" as a result of the early diagnosis, according to a 2014 study in the Journal of Cancer. Due to the test's low sensitivity and non-specificity, there is a far greater risk of incorrect diagnosis, unnecessary treatment, and a poorer quality of life.

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.

Instead, routine mammography remains 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 obtained through a simple blood draw. As such, the risks of the test are relatively small. Injection site pain, bruising, or bleeding is possible, as is lightheadedness 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 condition or response to therapy. This may include a complete blood count (CBC), liver functions tests, and kidney function tests. There are no preparations needed for any of these tests.


The blood draw takes only five minutes or so to perform. But, factoring in registration and waiting time, you may need to put aside anywhere from 30 to 90 minutes for the test.


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

What to Wear

Choose 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 advise the phlebotomist if you are taking Herceptin (trastuzumab) or any other mouse-derived monoclonal antibodies, as this can affect your results. If you are unsure whether a drug might affect your CA 27.29 test, speak with your oncologist.

Cost and Health Insurance

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

Speak with your insurance company to confirm what your copay 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 have to pay out of pocket, shop around for the best price. You should also ask your oncologist for information about any financial assistance programs that can aid in 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, although consent is generally implied when you arrived for a simple diagnostic procedure like a blood test.

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 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 then 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 place 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. Thereafter, 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 may want to keep it covered to prevent infection.

Although infection is rare, it can sometimes occur. Call your healthcare provider if you experience persistent 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 when levels of the CA 27.29 antigen are 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 greater than 38.6 U/mL can mean one of several things:

  • You have active cancer
  • That cancer may be spreading
  • That 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 a strong indication that a treatment is working, while increasing or stagnating values may suggest that treatment is not working.


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 be for reasons other than breast cancer, be them benign or cancerous. Such conditions include:


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

A Word From Verywell

The CA 27.29 test is an important tool for monitoring the treatment and care of people with metastatic breast cancer. But it is important to remember that the test has its limitations and is used solely to monitor your response to treatment and/or assess whether a cancer is active or spreading. 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.

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