There are several tumor markers associated with breast cancer. Testing for tumor markers can help a doctor get an idea of cancer activity in your body.

Breast cancer is one of the most common cancers affecting females around the world.

If you’ve received a breast cancer diagnosis, you may be familiar with testing for biomarkers like HER2 and hormone receptors. It’s also possible that a doctor will order tests for serum (blood) tumor markers during the course of your treatment.

Tumor markers can inform a doctor about the level of cancer activity in your body. Learn more about tumor marker tests in breast cancer, when doctors use them, and what the results can mean.

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Tumor markers are proteins that cancer cells produce, many of which are detectable in the blood. A doctor may order tumor marker tests to check whether the cancer treatment is working. Some examples of tumor markers in breast cancer are:

  • CA 15-3 and CA 27.29: These are two related markers that breast cancer cells make in higher amounts. As such, when a test detects them in the blood, they can signal the presence of breast cancer.
  • Carcinoembryonic antigen (CEA): CEA is a marker that doctors often use for colorectal cancer. However, they can also apply it to other types of cancer, including breast cancer.
  • CA 125: CA 125 is a marker most often associated with ovarian cancer but can also be a sign of breast cancer.

Additionally, parts of a tumor can sometimes break off and circulate in the blood. These circulating tumor cells (CTCs) can also act as a tumor marker. High amounts of CTCs in the blood can mean that cancer is growing and spreading, but they are typically not used as part of routine clinical practice.

Doctors can use tumor marker tests to gauge the level of cancer activity in your body. This information can be useful to evaluate how your cancer is responding to your current treatment.

Tumor marker tests can help inform treatment decisions. For example, an elevated tumor marker may indicate your current treatment isn’t working. A doctor may use this information, in addition to scans and how you feel, to decide when to switch or adjust your treatment.

While the results of a tumor marker test can be informative, they’re not conclusive. A low result doesn’t mean you don’t have cancer or are in remission.

For example, CA 15-3 shows the presence of metastatic breast cancer in 60% to 80% of people. This means that there’s a significant number of people who receive a normal tumor marker result while still having cancer.

Similarly, a high result doesn’t always mean cancer is growing and spreading or that your treatment isn’t working. That’s because it’s possible for various noncancerous conditions to cause elevated levels of some tumor markers.

As such, the American Society of Clinical Oncology doesn’t currently recommend the use of tumor markers for screening, diagnosis, or detecting cancer recurrence.

It does note that some tumor marker tests, such as those for CA 15-3/CA 27.29 and CEA, may be used along with other tests to guide treatment decisions in metastatic breast cancer.

Tumor marker tests for breast cancer can involve a simple blood draw, similar to the procedure you’d have during a routine physical.

What to expect during a tumor marker test

A healthcare professional will draw blood from a vein in your arm during the tumor marker test. The entire process only takes a few minutes. Here’s what you can expect:

  1. The person collecting your sample will sanitize the skin where the needle will go.
  2. They will tie a rubber band around your upper arm and ask you to make a fist. This helps the veins in your arm to stick out, making it easier to insert the needle.
  3. The needle will then go into a vein in your arm. A test tube at the top of the needle will collect the blood sample.
  4. The needle will be withdrawn from the vein once there is enough blood for the sample.
  5. A small amount of bleeding can occur afterward. You can apply pressure to the area with a piece of gauze.
  6. A bandage will then go over the gauze. You will typically need to leave this on for a few hours.

What to expect after a tumor marker test

Once your blood draw is complete, a lab will test it for tumor markers. A doctor will then receive the results and contact you to review them.

It’s possible to experience bruising or swelling in the area where you had your blood test. This will typically go away after a day or so.

The time it takes to receive your results depends on the laboratory doing the test. A doctor can let you know when to expect your results. When the results are ready, they’ll contact you to review them or discuss them at your next visit.

Since tumor markers are associated with cancer cells, higher results can be an indicator that:

  • your current treatment isn’t working effectively
  • a greater amount of cancer is present
  • your cancer is spreading to other areas

The table below shows the normal versus high test result values for some of the tumor markers noted earlier in this article.

Marker testNormalHigh
CA 15-3less than 30 units per milliliter (U/mL)30 U/mL or higher
CA 27-29less than 38 U/mL38 U/mL or higher
CA125less than 35 U/mLgreater than 35 U/mL
CEAless than 2.5 nanograms per milliliter (ng/mL)• Extensive disease: greater than 10 ng/mL
• Metastatic disease: greater than 20 ng/mL
CTCsN/Agreater than 5 CTCs per 7.5 mL of blood

It’s important to note that tumor marker tests aren’t conclusive. A doctor will also consider the results of other tests and your individual situation before deciding how to move forward.

Some examples of other tests include:

Several tumor markers are associated with breast cancer. Testing for tumor markers can help a doctor understand cancer activity in your body. The test involves collecting a sample of blood from a vein in your arm.

Tumor marker tests aren’t conclusive, so a doctor will also need to consider the results of other tests. If a doctor recommends a tumor marker test, be sure to discuss its various benefits and limitations beforehand.