Breast cancer is one of the most common cancers affecting women around the world. The National Cancer Institute estimates that there will be 281,550 new diagnoses of breast cancer in the United States in 2021.

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

Tumor markers can inform your doctor about the level of cancer activity in your body. Learn more about tumor marker tests in breast cancer, when they’re used, and what the results can mean.

Tumor markers are typically proteins that are produced by cancer cells, many of which can be found in the blood. Some examples of such tumor markers in breast cancer are:

  • CA 15-3 and CA 27.29: CA 15-3 and CA 27.29 are two related markers that are made in higher amounts by breast cancer cells. As such, when they’re found in the blood, they can signal the presence of breast cancer.
  • Carcinoembryonic antigen (CEA): CEA is a marker that’s often used for colorectal cancer. However, it can also be applied to other types of cancer as well, including breast cancer.
  • CA 125: CA 125 is a marker that’s most often associated with ovarian cancer, but can also be a sign of breast cancer.

Additionally, sometimes parts of a tumor can break off and circulate in the blood. These circulating tumor cells (CTCs) can also be used as a tumor marker. High amounts of CTCs in the blood can mean that cancer is growing and spreading.

Tumor marker tests can be used by doctors to gauge the level of cancer activity in your body. This information may be useful to:

  • evaluate how your cancer is responding to your current treatment
  • see if your cancer has spread to other areas (metastasized)
  • determine if a cancer that’s been in remission has come back (recurred)

Tumor marker tests can help to inform treatment decisions. For example, if a tumor marker is elevated, it may indicate that your current treatment isn’t working. Your doctor may use this information to switch or adjust your treatment.

Additionally, increased tumor markers can signal a cancer recurrence. This can prompt your doctor to start treatment again.

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 is elevated in less than 50 percent of people with early breast cancer and in 80 percent of people with metastatic breast cancer. 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.

They do 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.

Testing for tumor markers can also be expensive. A 2015 study of 39,650 people with early-stage breast cancer found that medical costs for those who had at least one tumor marker test were about 29 percent higher.

Lastly, receiving a high result can be distressing. The additional follow-up testing to determine the cause of the elevated markers can also lead to anxiety.

Regardless of your test results, additional tests will be needed to guide treatment decisions. It’s important to discuss tumor marker testing with your doctor to learn about benefits and limitations before being tested.

Tumor marker tests for breast cancer can be done using a simple blood draw, similar to what you’d have done during a routine physical. Here’s what to expect.

Preparing for a tumor marker test

There’s generally not any special preparation that you have to do prior to your blood draw. However, it may be a good idea to ask your doctor about prescription medications, over-the-counter drugs, or supplements that you’re taking.

What to expect during a tumor marker test

Blood will be drawn from a vein in your arm. The entire process only takes a few minutes. Here’s what you can expect:

  1. The person doing the blood draw will sanitize the area where the needle will be placed.
  2. A rubber band will be tied around your upper arm and you’ll be asked to make a fist. This helps to make the veins in your arm stick out, making it easier for the needle to be inserted.
  3. A needle will be inserted into a vein in your arm. This will be attached to a test tube that will collect the blood sample.
  4. Once the blood sample has been collected, the needle will be withdrawn from the vein.
  5. A small amount of bleeding can happen when the needle is removed. You’ll be asked to use a piece of gauze to apply pressure to the area.
  6. A bandage will then be placed over the gauze. Plan to leave the bandage on for a few hours.

What to expect after a tumor marker test

When your blood draw is over, your blood sample will be sent to a lab to be tested for tumor markers. The results will be sent to your doctor, who will contact you to go over them.

It’s possible that you’ll experience bruising or swelling in the area around where the needle was inserted. This will typically go away after a day or so.

The time that it takes to receive your results depends on the laboratory doing the test. Your doctor can let you know when to expect your results. When the results are ready, they’ll contact you to go over them.

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 mentioned earlier.

Marker testNormalHigh
CA 15-3Less than 30 U/mL30 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 ng/mLExtensive disease: Greater than 10 ng/mL Metastatic disease: Greater than 20 ng/mL
CTCsN/AGreater than 5 CTCs per 7.5 mL of blood

Remember that tumor marker tests aren’t conclusive by themselves. Because of this, your doctor will also consider the results of other tests as well as your individual situation before deciding how to move forward.

Some examples of other tests include:

There are several tumor markers that are associated with breast cancer. Testing for tumor markers can help your doctor to get an idea of cancer activity in your body. The test is done by collecting a sample of blood from a vein in your arm.

High levels of a tumor marker may indicate that a cancer is growing, spreading, or has recurred. This information can be used to help inform treatment decisions.

Because tumor marker tests aren’t conclusive by themselves, the results of other tests need to be considered along with them. If your doctor recommends a tumor marker test, be sure to discuss its various benefits and limitations beforehand.