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What is HER2 Testing & Why You Should Get It Done?

What is HER2?

HER2 or human epidermal growth factor receptor 2 is responsible for producing HER2 proteins that are present on the surface of breast cancer cells. On being activated these proteins signal the breast cancer cells to divide and multiply.

Normally, HER2 proteins play a role in the growth of breast cells, but when their gene is mutated, there is a production of too many HER2 proteins. This causes the uncontrolled growth and division of breast cells. This is seen occurring in about 1 in every 5 cases of breast cancer and is referred to as HER2-positive breast cancer(1).

What is HER2 Testing?

Why Should You Get HER2 Testing Done?

HER2 positive breast cancer is aggressive than the HER2 negative ones. They are also likely to recur.

Specially designed drugs are available for treating HER2 positive breast cancer and are also found effective.

If you are suffering from breast cancer, you need to know whether it is HER2 positive or not.

FISH and IHC Tests

To determine whether breast cancer is HER2 positive or not, testing is advised that is done on the tissue sample.

The two types of test are ISH or in-situ hybridization and IHC or immunohistochemistry.

In Situ Hybridization (ISH or FISH) Tests

An In situ hybridization looks at the genetics of the sample and the results are classified as positive, negative, or equivocal.

If the result is equivocal further testing known as Fluorescence in situ hybridization (FISH), which is a type of ISH, is done.

Sometimes IHC test is done first. If it proves to be inconclusive ISH test is performed. It has been found that the ISH test can confirm whether the cancer is HER2 positive or negative.

If the ISH test is done first and it is inconclusive, the IHC test is done or the ISH test is repeated.

In some cases, both IHC and ISH tests are needed to confirm the HER2 status.

Immunohistochemistry (IHC) Test

Immunohistochemistry (IHC) tests determine the quantity of HER2 protein receptors in breast cancer cells.

In an IHC test, the breast tissue is analyzed under a microscope. Special stains are used to see how many receptors are present in breast cancer cells. The readings are as follows(2):

  • A result showing 0 is negative
  • A result showing 1+ is also negative
  • A result showing 2+ is equivocal i.e. uncertain
  • A result showing 3+ is positive

No further testing is required if the result are 0 or 1+. A test showing 2+ is uncertain and required further testing.

How is HER2 Testing Done?

To diagnose the HER2 status, some breast tissue is removed for biopsy. Mild pain is experienced immediately after the biopsy. In most cases, doctors give anesthesia to minimize pain.

The tissue is sent to a pathology lab for review.

Make sure whichever lab your sample goes to is reputable and its HER2 testing kits are approved by the Food and Drug Administration (FDA).

Is HER2 Testing Safe And Accurate?

Both IHC and ISH testing techniques are safe. Mostly the testing is done from the original biopsy and would not require further procedures and can be completed in the doctor’s office or radiology rooms.

Scar tissue is developed around the biopsy site.

You can confirm from your doctor about the accuracy of the test. You can also ask for a second opinion from another pathologist.

HER2 targeted treatments are very effective in treating HER2 positive breast cancers, which are more aggressive than the other type. Also, the outlook of HER2 has improved over the years. It can be because of the new and effective treatment that specifically targets HER2 receptors.

If diagnosed with breast cancer make sure that the HER2 test is also performed. Also, if you were HER2 negative and the breast cancer has recurred, ask the doctor for the need to conduct a HER2 test. Breast cancers change status when they return. HER2-negative breast cancer may turn HER2 positive.

In HER2 positive cases, treatments are very effective. Always speak to your doctor about the disease and the test being performed and also the treatment options.

Pramod Kerkar, M.D., FFARCSI, DA
Pramod Kerkar, M.D., FFARCSI, DA
Written, Edited or Reviewed By: Pramod Kerkar, M.D., FFARCSI, DA Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:July 9, 2021

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