How the Cancer Antigen 27.29 Test Is Used to Monitor Breast Cancer

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lab worker analyzing blood test

Cancer antigen 27.29 (CA 27.29) is a blood test that is done specifically for people with breast cancer. It is one of the breast cancer tumor markers that can be used to monitor the course of the disease. One version of this test is called the " truquant BR radioimmunoassay test."

CA 27.29 is an antigen—that is, a specific type of protein present on the surface of cells and is produced by a gene called MUC-1. CA-27 is a "glycoproteins," (glyco means sugar) and may be present on the surface of epithelial cells like breast cancer cells. Breast cancer cells can shed copies of the CA 27.29 protein into the bloodstream too.

A blood CA 27.29 measurement is ordinarily less than 40 U/ml. With cancer, Ca-27 levels may increase, the higher the value, the greater the likelihood this may indicate the presence of cancer.


It can help to break down the different ways in which the CA 27.29 biomarker test may be used:

  • Diagnosis—This test is not often done to diagnose breast cancer, at least not alone. It's mentioned here to make note that the CA 27.29 test is the only blood test used specifically to determine the presence of breast cancer cells. If you have or think you may have early stage breast cancer, this test may be performed to help make your diagnosis.
  • To monitor treatments—The CA 27.29 test is often done to monitor your response to breast cancer treatments. If your levels rise, it may indicate that your cancer is coming back or progressing, and it may be necessary to adjust your treatments accordingly.  If your levels fall, it may indicate that your treatment is effectively killing your cancer.
  • To look for early recurrence—If your treatment for breast cancer has been completed, this test may be done at regular intervals to detect an early recurrence of your cancer. An elevation of CA 27.29 occurs, on average, around five months before a recurrence is evident based on symptoms or imaging studies alone. Despite this, there is still debate over whether or not finding a recurrence of cancer before symptoms makes a difference in the treatment and, ultimately, the outcome of the disease.
  • To monitor metastatic cancer (status check)—The test may help those with metastatic breast cancer know if their cancer is progressing. That said, elevated levels can linger for some time and, in one study, 30 percent of people had elevated levels which persisted for two to three months after the onset of effective treatment.

This test is not recommended as a method of screening for breast cancer, or as a way to diagnose breast cancer alone, as it lacks what scientists refer to as predictive value.

Moreover, physicians vary tremendously in their practice of ordering this test. Some physicians put little emphasis on the test, whereas others routinely order it on a regular basis. 


It's important to note the limitations of the CA 27.29 test. In monitoring the treatment of metastatic breast cancer—how this test is most commonly used—it’s important to again note that elevated levels of CA 27.29 may persist for up to three months after treatment has been completed.

In other words, if you have the test done a few months after finishing treatment, the levels could still be high even if you are responding well to the treatment.

Since the CA 27.29 test is the only test used specifically to detect the presence of breast cancer cells, it would seem that it would be ordered more often to screen for breast cancer. Yet, as noted, the test lacks predictive value in determining the presence of a breast cancer. 

Positive predictive value refers to the likelihood that you have a disease if you test positive for the disease. There are many tests in medicine that would seem to make sense as a method of screening for a disease, yet in studies, lack the accuracy to make a difference in survival rates.

The final limitation is when the test is used to find a recurrence. There is much debate over whether finding a recurrence of breast cancer early could make a difference. While, at first glance, it would seem that there would be benefits to this practice, studies have not found that survival rates improve when a recurrence of breast cancer is found early.

Part of the confusion lies in the goals of treatment for early-stage breast cancer versus metastatic breast cancer. With early stage breast cancer, the goal is usually to treat the disease aggressively in order to cure the cancer (or at least keep it from ever returning.) Aggressive treatment, however, is not the goal of metastatic breast cancer (though this may change in the near future) as it hasn't seemed to make a difference in survival rates. Instead, the goal is to usually use the least amount of treatment possible to control the disease.

A recent concern has arisen regarding the use of CA 27.29 in women who are receiving granulocyte stimulating therapy along with chemotherapy. A 2018 study found that women who received medications such as Neupogen or Neulasta to increase their white count following chemotherapy, as these treatments have been found to increase CA 27.29 levels.


The test is a simple blood test so the risks are small. Possible risks may include anxiety related to an abnormal test or a test result which does not accurately reflect the status of your cancer. 

Since this test is done as only a part of the workup monitoring cancer, the risk is often not of great concern. CA 27.29 is not a perfect test, but it is often useful along with other tests, such as imaging, to evaluate recurrence and response to treatment.

Causes of Elevated CA 27.29 Levels in Non-Breast Cancer Patients

Other cancers, as well as benign conditions, may result in an elevated level of CA 27.29. Cancers which may result in an elevated result include:

  • Lung cancer
  • Liver cancer
  • Pancreatic cancer
  • Colon cancer
  • Ovarian cancer
  • Prostate cancer

Benign conditions which can raise CA 27.29 include:

  • Ovarian cysts
  • Benign breast conditions of the breast and kidneys
  • Liver disease, such as cirrhosis—in one study, of people who had an elevation of CA 27.29 but did not have cancer, the cause was cirrhosis 25 percent of the time

In addition to CA 27.29, there are other tumor markers which may be used to monitor breast cancer. These include: 

  • Cancer antigen 15-3 ( CA 15-3)
  • Carcinoembryonic antigen (CEA)

KI-67 is not used to monitor breast cancer.

Most often, either the CA 27.29 test or the CA 15-3 test will be ordered, but not both.

A Word From Verywell

The CA 27.29 may be used for several different purposes with breast cancer and is the one biomarker used specifically to determine the presence of breast cancer cells. That said, there are other cancers as well as benign conditions which can lead to elevated levels.

It is also important to understand the limitations of the test when used to evaluate breast cancer, including reasons the level may be abnormally elevated, such as when medications such as Neupogen or Neulasta are used. And the test should always be used in conjunction with other findings, such as a physical exam, other blood tests, and imaging studies.

In summary, the value of this test for women with breast cancer is that it may provide information and guide you and your doctor as to:

  • Your response to treatment
  • The status of your cancer
  • The possibility of early recurrence
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