What is HER2 breast cancer testing?
HER2 stands for human epidermal growth factor receptor 2. It is a gene that makes a protein found on the surface of all breast cells. It is involved in normal cell growth.
Genes are the basic units of heredity, passed down from your mother and father. In certain cancers, especially breast cancer, the HER2 gene mutates (changes) and makes extra copies of the gene. When this happens, the HER2 gene makes too much HER2 protein, causing cells to divide and grow too fast.
Cancers with high levels of the HER2 protein are known as HER2-positive. Cancers with low levels of the protein are known as HER2-negative. About 20 percent of breast cancers are HER2-positive.
HER2 testing looks at a sample of tumor tissue. The most common ways to test tumor tissue are:
- Immunohistochemistry (IHC) testing measures the HER2 protein on the surface of the cells
- Fluorescence in situ hybridization (FISH) testing looks for extra copies of the HER2 gene
Both types of tests can tell whether you have HER2-positive cancer. Treatments that specifically target HER2-positive breast cancer can be very effective.
Other names: human epidermal growth factor receptor 2, ERBB2 amplification, HER2 overexpression, HER2/neu tests
What is it used for?
HER2 testing is mostly used to find out whether cancer is HER2-positive. It is also sometimes used to see if cancer is responding to treatment or if cancer has returned after treatment.
Why do I need HER2 breast cancer testing?
If you’ve been diagnosed with breast cancer, you may need this test to find out if your cancer is HER2-positive or HER2-negative. If you are already being treated for HER2-positive breast cancer, you may need this test to:
- Find out if your treatment is working. Normal levels of HER2 may mean you are responding to treatment. High levels may mean the treatment is not working.
- Find out if cancer has come back after treatment.
What happens during a HER2 breast cancer test?
Most HER2 testing involves taking a sample of tumor tissue in a procedure called a biopsy. There are three main types of biopsy procedures:
- Fine needle aspiration biopsy, which uses a very thin needle to remove a sample of breast cells or fluid
- Core needle biopsy, which uses a larger needle to remove a sample
- Surgical biopsy, which removes a sample in a minor, outpatient procedure
Fine needle aspiration and core needle biopsies usually include the following steps:
- You will lay on your side or sit on an exam table.
- A health care provider will clean the biopsy site and inject it with an anesthetic so you won’t feel any pain during the procedure.
- Once the area is numb, the provider will insert either a fine aspiration needle or core biopsy needle into the biopsy site and remove a sample of tissue or fluid.
- You may feel a little pressure when the sample is withdrawn.
- Pressure will be applied to the biopsy site until the bleeding stops.
- Your provider will apply a sterile bandage at the biopsy site.
In a surgical biopsy, a surgeon will make a small cut in your skin to remove all or part of a breast lump. A surgical biopsy is sometimes done if the lump can’t be reached with a needle biopsy. Surgical biopsies usually include the following steps.
- You will lie on an operating table. An IV (intravenous line) may be placed in your arm or hand.
- You may be given medicine, called a sedative, to help you relax.
- You will be given local or general anesthesia so you won’t feel pain during the procedure.
- For local anesthesia, a health care provider will inject the biopsy site with medicine to numb the area.
- For general anesthesia, a specialist called an anesthesiologist will give you medicine so you will be unconscious during the procedure.
- Once the biopsy area is numb or you are unconscious, the surgeon will make a small cut into the breast and remove part or all of a lump. Some tissue around the lump may also be removed.
- The cut in your skin will be closed with stitches or adhesive strips.
The type of biopsy you have will depend on different factors, including the size and location of the tumor. HER2 can also be measured in a blood test, but blood testing for HER2 has not been proven to be useful for most patients. So it is not usually recommended.
After your tissue sample has been taken, it will be tested in one of two ways:
- HER2 protein levels will be measured.
- The sample will be looked at for extra copies of the HER2 gene.
Will I need to do anything to prepare for the test?
You won’t need any special preparations if you are getting local anesthesia (numbing of the biopsy site). If you are getting general anesthesia, you will probably need to fast (not eat or drink) for several hours before surgery. Your surgeon will give you more specific instructions. Also, if you are getting a sedative or general anesthesia, be sure to arrange for someone to drive you home. You may be groggy and confused after you wake up from the procedure.
Are there any risks to the test?
You may have a little bruising or bleeding at the biopsy site. Sometimes the site gets infected. If that happens, you will be treated with antibiotics. A surgical biopsy may cause some additional pain and discomfort. Your health care provider may recommend or prescribe medicine to help you feel better.
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
What do the results mean?
If HER2 protein levels are higher than normal or extra copies of the HER2 gene are found, it probably means you have HER2-positive cancer. If your results show normal amounts of HER2 protein or the normal number HER2 genes, you probably have HER2-negative cancer.
If your results were not clearly positive or negative, you will probably get retested, either using a different tumor sample or using a different testing method. Most often, IHC (testing for the HER2 protein) is done first, followed by FISH (testing for extra copies of the gene). IHC testing is less expensive and provides faster results than FISH. But most breast specialists think FISH testing is more accurate.
Treatments for HER2-positive breast cancer can substantially shrink cancerous tumors, with very few side effects. These treatments are not effective in HER2-negative cancers.
If you are being treated for HER2-positive cancer, normal results may mean you are responding to treatment. Results that show higher than normal amounts may mean your treatment is not working, or that cancer has come back after treatment.
Is there anything else I need to know about HER2 breast cancer testing?
While it’s much more common in women, breast cancer, including HER2-positive breast cancer, can also affect men. If a man has been diagnosed with breast cancer, HER2 testing may be recommended.
In addition, both men and women may need HER2 testing if they have been diagnosed with certain cancers of the stomach and esophagus. These cancers sometimes have high levels of the HER2 protein and may respond well to HER2-positive cancer treatments.