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HER2 Diagnosis and Tests

Updated on February 01, 2022
Medically reviewed by
Mark Levin, M.D.
Article written by
Maureen McNulty

  • Breast cancers with a higher-than-normal level of HER2 protein are known as HER2-positive. Knowing whether your breast cancer is HER2-positive or HER2-negative helps you understand more about your outlook and possible treatments.
  • Diagnostic testing for both breast cancer and genetic changes in HER2 levels begins with a biopsy. HER2 can also be evaluated with a blood test.
  • Tests such as immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) can measure levels of HER2 protein and count copies of the HER2 gene.

Most people with breast cancer will undergo tests to determine whether their cancer is HER2-positive or HER2-negative. It’s important to find out this information as early as possible, because your HER2 status tells you and your doctor which treatments are most likely to work.

About 20 percent of people with breast cancer have HER2-positive tumors. This means their cancer cells have many copies of the HER2 gene (also called human epidermal growth factor receptor 2, HER2/neu, or ERBB2).

Read more about the HER2 gene, HER2 protein, and breast cancer prognosis.

Breast Cancer Diagnosis

Receiving a breast cancer diagnosis often begins with discovering a mass or lump. This may happen during a doctor’s appointment, a breast self-examination, or a routine mammogram screening for breast cancer.

Imaging tests, such as ultrasound or magnetic resonance imaging (MRI), may be used to further examine the lump, but they can’t diagnose whether or not a mass is cancerous.

Biopsy

A biopsy is the first step in both breast cancer diagnosis and HER2 testing. During a biopsy, your doctor will take a small sample of tissue from your breast for microscopic study. A biopsy helps the doctor tell whether or not you have cancer, and if so, what type and how advanced it is. Biopsy tissue can also show which genetic changes are present in your cancer cells, which can help the doctor determine the best treatment plan.

There are a few ways a doctor can remove a sample of cells. They may recommend a specific type of biopsy based on factors like how large the mass is, its location within the breast, and your own personal preferences.

Needle-Based Biopsies

If your doctor suspects breast cancer, they will probably recommend a core needle biopsy. During this procedure, the doctor will numb part of the breast, make a small cut into your skin, and remove multiple small cylinder-shaped pieces of breast tissue using a hollow needle.

Another possible biopsy option is a fine needle aspiration (FNA). This procedure also involves using a needle, but the needle is generally thinner and removes fewer cells. You may not receive any numbing medication for FNA, because it is usually quick and doesn’t hurt very much.

During needle-based biopsies, the doctor needs to make sure they are putting the needle into the right area and removing the right tissue. They may do this by feeling for the lump, or they may use additional imaging tests to guide the needle.

After the biopsy, the doctor may put a dressing over the area. The affected area usually doesn’t take too long to heal, but there may be some swelling or bleeding at first. Follow your doctor or nurse’s instructions to take care of the biopsy area.

Surgical Biopsy

Surgical breast biopsies aren’t as common as core needle biopsies or FNAs. They may be used in cases where a needle biopsy can’t reach the affected tissue, or if the results of a needle biopsy are unclear.

During a surgical breast biopsy, a doctor will remove all or part of the breast lump. The procedure usually takes place in a hospital, and you will probably be given medicine to make you sleepy and help you not feel the pain.

After the Biopsy

In most cases, a biopsy will show that there is no cancer. However, if you do have cancer, the biopsy will give the doctor more information about what type of cancer cells are present. A biopsy can also help the doctor find out how advanced your breast cancer is and assign it a stage and grade.

After your biopsy sample is taken, it will be sent to a laboratory, where it will be studied by a doctor called a pathologist. Usually, it will take a few days to get your biopsy results back. Your doctor can give you a better idea of when results may be available and how you can see them.

Are you living with HER2-positive breast cancer?
What was your diagnostic process like?
Click here to share your experience in the comments below.

Laboratory Tests

What does the pathologist do with your biopsy sample? They may look for several factors, including proteins such as HER2.

Viewing Cells Under a Microscope

The pathologist will likely place some of the cells on a glass slide and use a microscope to view them more closely to determine whether they are cancerous. Cancer cells are more likely to have unusual shapes and sizes. Additionally, normal cells are usually arranged in a neat order. Cancer cells, on the other hand, are disorganized, form unusual-looking structures, and start growing in nearby tissues. Looking for these features helps pathologists recognize whether the cells in the biopsy sample are normal or cancerous.

A pathologist can assign a breast cancer grade based on how the cells appear. When cancer cells don’t look too unusual, they are lower-grade, meaning they are expected to grow more slowly. When the cancer cells look very different from normal breast cells, they are higher-grade. Your doctor can use information about your cancer’s grade along with your HER2 status to estimate your outlook and determine which treatments may be most helpful.

Immunohistochemistry

A common method used by pathologists to study biopsy samples is an immunohistochemical stain. This test can help doctors tell whether your cancer cells contain high levels of HER2 or other proteins.

To perform this HER2 test, the pathologist will attach some of the tissue sample from the biopsy to a glass slide. They will then add a mixture of chemicals containing an antibody. An antibody is a molecule that can recognize and attach to a specific protein. If the cells contain this protein, the antibody will attach and the cells will change color. By using an anti-HER2 antibody that recognizes the HER2 protein, a pathologist can see how much of this protein the breast cancer cells have.

The more HER2 protein is found on the cells, the darker the cells will look. The pathologist will report your IHC results as a number.

  • A result of 0 or 1+ means the cells have no or very little HER2, and the cancer is considered HER2-negative.
  • A result of 2+ shows the cells have some HER2, but it is not clear if the cancer should be considered negative or positive.
  • A result of 3+ means the cells have a lot of HER2, and the cancer is considered HER2-positive.

IHC may also be used to test for other cancer-related proteins in your biopsy sample, including estrogen receptors.

Fluorescence In Situ Hybridization

If your IHC test results for HER2 are 2+, also called “equivocal,” you will probably need to have another laboratory test called fluorescence in situ hybridization. In this case, you usually won’t need to have additional procedures done. The pathologist can use cells from your original biopsy sample.

FISH testing also measures the amount of HER2 within your breast cancer cells. However, while IHC tests for protein overexpression (high levels of the HER2 protein), FISH tests for HER2 gene amplification (lots of copies of the HER2 gene). FISH may be more accurate than IHC, but FISH can cost more and take longer to process.

Chromogenic In Situ Hybridization

Most people with breast cancer will have IHC and/or FISH tests to determine whether their cancer is HER2-positive or HER2-negative. However, in some cases, other types of in situ hybridization may be used.

Chromogenic in situ hybridization (CISH) is occasionally used instead of FISH. Like FISH, CISH uses pieces of DNA to count how many copies of the HER2 gene can be found in cells. The more HER2 genes your cells have, the more the cells will change color during the test.

CISH is thought to be just as accurate as FISH, but it may be less expensive. However, not as many laboratories use this method.

What Happens After Your HER2 Test?

Once you have your HER2 results, your doctor should talk to you about the next steps. Breast cancers that are HER2-positive often respond very well to targeted therapies — medications that identify and attack cells with the HER2 protein. If you have HER2-positive breast cancer, your doctor will probably recommend that you use targeted therapies.

Read more about treatment options for HER2-positive breast cancer.

At some point after you begin receiving breast cancer treatment, your doctor may have you undergo more HER2 testing. Results can help show whether the treatment is working. If you were diagnosed with HER2-positive cancer, and later tests show that your HER2 levels are normal, this may mean your tumor is shrinking. High HER2 levels, on the other hand, may indicate that your cancer has come back.

Talk With Others Who Understand

MyBCTeam is the social network for people with breast cancer. On MyBCTeam, members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Are you living with HER2-positive breast cancer? What was your diagnostic process like? Share your experience in the comments below, or start a conversation by posting on your Activities page.

All updates must be accompanied by text or a picture.
Mark Levin, M.D. is a hematology and oncology specialist with over 37 years of experience in internal medicine. Review provided by VeriMed Healthcare Network. Learn more about him here.
Maureen McNulty studied molecular genetics and English at Ohio State University. Learn more about her here.

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