HER2 Tumor Marker Test

What is HER2 tumor marker testing?

HER2 tumor marker tests look for the tumor marker called human epidermal growth factor receptor 2 (HER2). Tumor markers are substances made by cancer cells. HER2 is also sometimes called HER2/neu. 

Normally, HER2 plays a role in cell growth. However, some types of cancer cells make larger than usual amounts of it. A HER2 tumor marker test usually uses a sample of tumor tissue to measure either:

• The amount of HER2 protein on the surface of cancer cells
• How many copies of the HER2 gene are inside the cancer cells

Genes are parts of DNA in your cells that you inherit from your parents. HER2 genes have instructions for making the HER2 protein. Normally, most cells have two copies of the HER2 gene, one from each parent. But certain cancers develop extra copies of this gene, which leads to too much HER2 protein on the cancer cells.

Cancers with large amounts of HER2 protein tend to grow quickly and spread to other parts of the body. Certain medicines, called HER2 targeted therapies, can block or slow HER2 proteins by attacking cancer cells that have certain amounts of them.

Health care providers may use different types of HER2 tumor marker tests. The most common are:

• IHC (immunohistochemistry staining assay), which measures the amount of HER2 protein on cancer cells
• FISH (fluorescence in situ hybridization), which checks for extra copies of HER2 genes in cancer cells

For some cancers, an IHC test is often done first because it's faster and less expensive.

Other names: human epidermal growth factor receptor 2, ERBB2 amplification, HER2 overexpression, HER2/neu tests

What is it used for?

HER2 tumor marker tests are used to learn how much HER2 protein is present in cancer cells or whether the cancer cells have extra copies of the HER2 gene. The results can help your provider decide whether certain medicine that target HER2 proteins may be helpful.

Some HER2-targeted medicines work best when cancer cells have high levels of HER2. However, newer medicines can help some cancers that have lower levels of the tumor marker.

HER2 testing is commonly used for certain cancers of the:

• Breast
• Stomach
• Esophagus (the muscular tube that carries food and liquids from your mouth to the stomach)

HER2 testing may also be considered for some other cancers if your provider thinks HER2 proteins or gene copies could affect treatment. These cancers include those of the:

• Ovaries
• Bladder
• Pancreas

Why do I need HER2 tumor marker testing?

You may need HER2 tumor marker testing to help guide cancer treatment decisions if you have breast cancer that has:

• Just been diagnosed and is growing in the normal breast tissue around the tumor. This is called “invasive” cancer.
• Spread beyond your breast and is growing in other parts of your body. This is called metastatic cancer. Your provider may recommend testing a sample of the cancer tissue outside of the breast to see whether its HER2 levels differ from those in the original breast tumor. This information may help guide treatment.
• Come back after treatment, usually after a period of time when no cancer could be found in your body. This is called recurrent cancer. Your provider may recommend testing the new tumor for HER2, even if the old tumor was HER2-negative. That's because HER2 status can sometimes be different when cancer comes back.

You may also need HER2 tumor marker testing if you have:

• Stomach or esophageal cancer that can't be removed using surgery or has come back after treatment
• Cancer of the pancreas, bladder, ovaries, or certain other cancers that may have high levels of HER2 and that may benefit from targeted therapy

What happens during a HER2 tumor marker test?

Most HER2 testing uses a sample of tumor tissue. The tissue will be removed during a procedure called a biopsy. A biopsy is the procedure of removing and examining tissue, cells, or fluids from the body. There are many ways to do a biopsy. The type of biopsy you have depends on where the tumor is located. In general, a biopsy may be done using:

• A hollow needle inserted through your skin. Imaging tests, such as ultrasound, may be used to guide the needle:
  • A fine needle aspiration biopsy uses a very thin needle to remove a sample of cells and/or fluid.
  • A core needle biopsy uses a larger needle to remove a sample.
• Surgery. A surgeon may remove a sample of the tumor (incisional biopsy) or the entire tumor (excisional biopsy).
• Endoscopy. This procedure uses a scope to look inside your body. Special tools may be used with a scope to remove a tissue sample. An endoscopy may be used for a biopsy of a tumor in your stomach or esophagus.

Will I need to do anything to prepare for the test?

Preparations for your test depend on how your tissue sample will be taken. Ask your provider how to prepare for your test.

If you are getting medicine to relax or sleep during the procedure, you will probably need to fast (not eat or drink) for several hours before surgery. You will also need to have someone take you home, because you may be sleepy after the procedure.

Are there any risks to the test?

Risks depend on how your tissue sample is taken. In general, if you are having a biopsy, you may have a little bruising or bleeding where the tissue was removed. Ask your provider to explain any risks from a biopsy.

What do the results mean?

The results of HER2 tumor marker tests are reported differently, depending on the type of test you had.

IHC test results for cancer of the breast, stomach, or esophagus show the amount of HER2 protein as a score:

• 0 (zero) or 1+ means that your cancer cells don't have high levels of HER2 protein. In breast cancer, these results are considered HER2-negative. However, some breast cancers with these results may have low levels of HER2 (sometimes called HER2-ultralow or HER2-low) that your provider can treat with certain newer medicines.
• 2+ means that the amount of HER2 protein is borderline. This may be reported as “equivocal,” which means the test result is not clear. You may need a different type of test, such as a FISH test, to see if your cancer is HER2 positive.
• 3+ means that your cancer cells have high levels of HER2 protein. Your cancer is HER2 positive.

FISH results for cancer of the breast, stomach, or esophagus will be reported as either:

• HER2 negative, which means the test did not find enough extra copies of the HER2 gene for the cancer to be HER2-positive. However, like with IHC testing, HER2 negative results don't necessarily mean that the cancer has no HER2 protein.
• HER2 positive, which means the test found enough extra copies of the HER2 gene for the cancer to be HER2-positive. HER2 targeted therapy will likely be useful in treating your cancer.

Your provider will consider your HER2 results along with other information about your cancer when choosing treatment. Talk with your provider to learn what your results mean.

Learn more about laboratory tests, reference ranges, and understanding results.