What is HER2 Testing?

What is HER2-positive breast cancer?1

HER2(human epidermal growth factor receptor 2) is a growth-promoting protein present on the outside of all breast cells. Breast cancer cells with higher than normal levels of HER2 are called HER2-positive.

Why is the HER2 status test done?2

HER2 (human epidermal growth factor receptor 2) is a gene that can play a role in the development of breast cancer. Information about HER2 status can tell you whether or not HER2 is playing a role in the cancer.

Methods of HER2 testing1,2

There are several tests used to find out if breast cancer is HER2-positive. Two commonly used tests are:

    These characteristics include:1
  • IHC test or the Immuno- Histo- Chemistry test which uses a chemical dye to stain the HER2 proteins.2
  • FISH test or the Fluorescence In Situ Hybridization test which uses special labels that attach to the HER2 proteins and change their color.2

FISH is more expensive and takes longer to get the results. Often the IHC test is done first.1,2

What do the test results mean?1

Interpreting the IHC test result score:1

IHC Score HER2-positive or negative Treatment / Course of Action
0 or 1+ HER2-negative Does not respond to treatment with drugs that target HER2
3+ HER2-positive Usually treated with drugs that target HER2
2+ Equivocal / unclear HER2 status needs to be clarified/ futher testing required

With the FISH test, you get a score of either positive or negative (some hospitals call a negative test result “zero”).2

Significance of HER2 positive breast cancer1

HER2 positive breast cancers tend to grow and spread faster than other breast cancers, but are more likely to respond to treatment with drugs that target the HER2 protein.

  1. Breast Cancer HER2 Status Available at https://www.cancer.org/cancer/breast-cancer/understanding-a-breast-cancer-diagnosis/breast-cancer-her2-status.html Accessed on 28 July 2021
  2. HER2 Status Available at https://www.breastcancer.org/symptoms/diagnosis/her2 Accessed on 28 July 2021