Breast Cancer Tumor Marker Tests

CA 15-3, CA 27.29, CEA, and others

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Breast cancer tumor markers are substances produced by cancer cells or by your body in response to cancer. Doctors can test you for markers including cancer-antigen (CA) 15-3, CA 27.29, CEA, CA-125, and circulating tumor cells (CTCs). They can be used to monitor the progression of cancer, evaluate the response to treatment, or discover a recurrence. They also may be able to predict who will have a late recurrence.

Still, these tests do have limitations, as not all cancers cause an elevation in marker levels, and when the levels are elevated, it may be due to a different condition. Therefore, tumor marker tests are not used alone to evaluate or plan breast cancer treatment, but they may be helpful alongside other tests such as imaging studies.

Receptor tests such as estrogen receptor and HER2 receptor tests are considered biomarkers, but they're used differently than tumor marker tests.

breast cancer tumor marker test
Verywell / Brianna Gilmartin

Purpose of Tests

Tumor markers can be detected in blood or urine. Some tumor marker tests are only used for people with breast cancer, whereas others may be used for people with a number of different cancers.

Breast cancer tumor marker tests may be used for a number of different reasons and in a variety of settings, including screening for cancer, monitoring progression (especially with metastatic breast cancer), identifying recurrence, and monitoring treatment response. There are several tumor marker tests available, with CA 15-3 and CA 27.29 being those most commonly used at the current time.

One Piece of the Puzzle

Tumor marker tests can be, but are not ordinarily used to screen for or diagnose breast cancer. Even if the tests are done, they must be interpreted along with other tests.

Cancer Antigen 15-3

Cancer antigen 15-3 (CA 15-3) is a protein produced by both normal and cancerous breast cells. CA 15-3 is released into the bloodstream when these cells break down.

The test has limitations, in that increased levels are only found in 30% of people with early stage breast cancer and 50% to 90% of people with metastatic breast cancer. Levels may also be increased due to non-breast-cancer-related conditions, such as cirrhosis, lupus, pelvic inflammatory disease, and much more.

The CA 15-3 test may be used to:

  • Screen for recurrence: Increasing levels may mean breast cancer has returned.
  • See if breast cancer is progressing: Increasing levels may mean that breast cancer is worsening. Levels tend to be particularly high when breast metastasizes (spreads) to the bones or liver.
  • To monitor the response to treatment: If levels are decreasing, it can indicate that treatments are working. However, exceptions exist (see "Limitations" below), and levels often take between four and six weeks to decrease when a tumor is shrinking in size.

Cancer Antigen 27.29 (TRU-QUANT)

Cancer antigen 27.29 (CA 27.29) is a glycoprotein found on the surface of epithelial cells such as breast cancer cells. Levels may be increased in people with breast cancer, but also with cancers such as lung cancer, colon cancer, and ovarian cancer, as well as benign conditions like ovarian cysts and liver disease.

The CA 27.29 test may be used to:

  • Supplemental diagnostic testing: While never used alone, it may be used as an added test in making the diagnosis of breast cancer.
  • Monitor for recurrence: Increasing levels of CA 27.29 might mean a recurrence of breast cancer, and levels often begin to increase around five months before signs of a recurrence are noted. Still, it's not certain whether detecting a recurrence early can make any difference in long-term survival.
  • Monitor for progression: Increasing levels often mean cancer is progressing.
  • Evaluate the response to treatment: If a treatment is working, levels often decrease.

In general, the CA 27.29 test provides information that is very similar to the CA 15-3 test, and most of the time, only one of these tests will be ordered. Your doctor may refer to this test by the brand name TRU-QUANT.

Cancer Antigen-125

Cancer antigen 125 (CA-125) is more commonly known for monitoring ovarian cancer, but it may be used as a test to monitor breast cancer as well.

Carcinoembryonic Antigen

Carcinoembryonic antigen (CEA) is present in small amounts in everyone's blood, but levels can be elevated with a number of different cancers, including those of the breast, colon, pancreas, and more, as well as in several benign conditions. Levels are also increased in people who smoke.

The use of the CEA test during chemotherapy is problematic because the treatment often causes levels to rise, even if the chemo is effective at breaking down the cancer cells.

Circulating Tumor Cells (CTCs)

When a tumor is present, some cells continually break off and absorb into the bloodstream. A test for circulating tumor cells identifies these. The CellSearch CTC test is most often used for people who have metastatic breast cancer, and it may have a place in guiding treatment decisions, such as whether or not to use single therapy.

Though still investigational, CTC results may be used down the line to predict who will have a late recurrence of breast cancer. For women who have estrogen receptor-positive breast cancer, roughly 50% of recurrences develop at least five years after the initial diagnosis. Researchers have found that when CTCs are detected five years after diagnosis, the chance of recurrence is 21.7 times higher than when they're not detected.

In the future, the test could be used to help answer questions like how long medications such as aromatase inhibitors should be continued.

Limitations

Tumor-marker testing for breast cancer does come with several limitations, including false negatives and false positives.

A false positive is a result that indicates a problem when there isn't one. That leads to anxiety and the possibility of over-treatment. A false negative occurs when a test is normal, but cancer is actually present or growing.

These tests can also be very expensive and may or may not be covered by insurance.

Some treatments can cause the results of tumor marker tests to be inaccurate. For example, treatment with the drug Afinitor (everolimus) causes CA 15-3 test results to be the opposite of what they should be.

These tests may also not reflect what is actually happening with cancer, as levels may take several weeks and sometimes up to three months (with CA 27.29) to reflect changes.

Finally, human error, such as an incorrectly taken specimen or lab error can lead to erroneous results.

Testing

When your oncologist recommends a tumor marker test, they will explain why the test may be helpful, what the results may mean, as well as the test's limitations.

Preparation

There is no specific preparation needed for these tests.

During the Test

Tumor marker tests are done through a simple blood draw, although for those who have had chemotherapy, this is not always so simple. The sample can be collected via a port or a pic-line, if you have one.

After the Test

Tumor marker tests vary in terms of the time it takes to receive results. Ask your doctor when you can expect to get yours, whether you'll be contacted about them, or if you need to make an appointment to go over them with your doctor.

Breast Cancer Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

Doctor Discussion Guide Woman

Interpreting Results

The results of tumor-marker tests can't be properly interpreted without findings from a physical exam and imaging studies. They're just one piece of the overall picture.

Tumor Marker Normal Range
CA 15-3 Less than 30 units/mL
CA 27.29 Less than 38 units/mL
CA-25 0 to 35 U/m
CEA Less than 2.5 ng/mL (non-smokers), less than 5 ng/mL (smokers)
Circulating tumor cells 0 (if no evidence of cancer is present); change over time is usually more important than the absolute level in those with metastatic cancer

A Word From Verywell

Learning about your cancer and being your own advocate in your care can help you feel more in control of your disease, and sometimes, it may even make a difference in your outcome. Play an active role in your care. Keep asking questions. Treatment and monitoring of breast cancer are improving rapidly, and it's hard for any one person, even a specialist, to stay on top of every change.

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