What is HER2 tumor marker testing?

Tumor marker tests look for substances, called tumor markers, that are often made by cancer cells or normal cells in response to cancer. The test results can provide important information, such as how fast a cancer may grow and which treatments are most likely to work.

HER2 is a type of tumor marker. It stands for human epidermal growth factor receptor 2. It's also called HER2/neu. HER2 is a protein involved in normal cell growth. Some types of cancer cells make larger than normal amounts of HER2, including certain cancers of the breast, stomach, and esophagus.

Cancers with large amounts of HER2 protein tend to grow quickly and spread to other parts of the body. Certain medicines, called HER2 targeted therapy, can block or slow HER2 proteins and help control these cancers. But these medicines won't help cancers that don't have high levels of HER2 proteins. So, HER2 tumor marker testing is necessary to find out if targeted therapy will be helpful.

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, you have two HER2 genes in each cell, one from each parent. But certain cancers have extra copies of the HER2 gene, which leads to too much HER2 protein on the cancer cells.

A HER2 tumor marker test looks to see whether certain cancers are:

• HER2 positive, which means the cancer has high levels of the HER2 protein or HER2 genes. These cancers are likely to respond to HER2 targeted therapy.
• HER2 negative, which means your cancer cells have little to no HER2 protein or a normal number of HER2 genes. This type of cancer may grow more slowly than HER2-positive cancer. It is also less likely to come back after treatment or spread to other parts of the body. HER2 targeted therapy will not work for this type of cancer, but other treatment options may help.

There are different HER2 tumor marker tests for checking HER2 proteins and HER2 genes. Usually, a protein test is done first because those tests are faster and less expense. Blood tests to measure HER2 usually aren't recommended. That's because it's not clear how blood test results can plan cancer treatment.

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 mostly used to find out whether certain cancers are HER2 positive or negative. This information shows how fast cancer may grow and whether medicine to target HER2 proteins may be helpful.

HER2 tumor marker testing is mainly used for cancers that start in the:

• Breast (most common)
• Stomach
• Esophagus
• 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. The cancer growing outside of your breast should be tested to see if it's HER2 positive, even if your breast tumor was already tested.
  • Come back after treatment, usually after a period of time when no cancer could be found in your body. This is called recurrent cancer. The new tumor should be tested to see if it's HER2 positive even if your first tumor was tested. That's because cancer cells can change over time.
• Stomach or esophageal cancer that:
  • Can't be removed using surgery.
  • Has come back after treatment.
• Cancer of the pancreas, bladder, ovaries, or certain other cancers that may have high levels of HER2 which may be treated with medicines that target HER2.

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. 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 health care 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 the test you're having.

What do the results mean?

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

• IHC (immunohistochemistry staining assay) to measure the amount of HER2 protein on cancer cells
• FISH (fluorescence in situ hybridization) to check for extra copies of HER2 genes in cancer cells

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 too much HER2 protein. Your cancer is HER2 negative and will not respond to HER2 targeted therapy. Your provider will discuss other treatment options.
• 2+ means that the amount of HER2 protein is borderline. This may be reported as "equivocal." It means the test result is not clear. You may need to have a different type of HER2 tumor marker test. The test may be done on the same tissue sample, or you may need to provide a new sample.
• 3+ means that your cancer cells have too much HER2 protein. Your cancer is HER2 positive and is likely to respond to HER2 targeted therapy.

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

• HER2 negative, which means that you don't have too many HER2 genes in your cancer cells. HER2 targeted therapy won't help your cancer, so your provider will discuss other treatment options.
• HER2 positive, which means that your cancer cells have too many HER2 genes. HER2 targeted therapy is likely to help your cancer.

Talk with your provider to learn what your results mean for your treatment.

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