Tumor markers are substances, often proteins, produced by cancer cells or by your body in response to cancer. These include cancer-antigen (CA) 15-3, CA 27.29, CEA, CA-125, and circulating tumor cells (CTCs).
This article will explain why tumor markers are tested for breast cancer diagnostics, what types of tests are available, what to expect from the test, and how to interpret the results.
What Are Tumor Marker Tests?
Tumor marker tests are blood tests used to detect certain cancer markers, which may help to diagnose breast cancer. The test results also tell your oncologist if the disease is being held at bay with current treatments or is likely to spread or recur.
Why They Are Used in Breast Cancer
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, cancer that has spread), identifying recurrence, and monitoring treatment response. There are several tumor marker tests available, with CA 15-3 and CA 27.29 being the ones most commonly used.
Types of Tumor Marker Tests
There are several tumor marker tests that your healthcare provider will order depending on the type of information they are seeking.
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 cancer cells break down.
The test has limitations, in that increased levels are not found in everyone with breast cancer. Levels may also be increased due to conditions not related to breast cancer, such as cirrhosis, lupus, and pelvic inflammatory disease.
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 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 the Limitations section 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:
Supplement 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 healthcare provider 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 several different cancers, including those of the breast, colon, and pancreas, as well as in several benign conditions. Elevated CEA in breast cancer may indicate a poor outcome.
It can be used for the following purposes:
To monitor cancer treatmentsTo identify recurrencesTo stage cancer To see if cancer has spread to other areasTo estimate prognosis
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 to use a 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. As of 2018, 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 overtreatment. A false negative occurs when a test is normal, but cancer is 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 a 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 and 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 (port-a-cath, a catheter inserted into your chest or upper arm) or a PICC line (peripherally inserted central catheter, a long tube inserted through a vein in your arm), if you have one.
After the Test
Tumor marker tests vary in terms of the time it takes to receive results. Ask your healthcare provider 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 healthcare provider.
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.
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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 along with other tests such as imaging studies.
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. 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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