HER2 (Human Epidermal Growth Factor Receptor 2)

HER2 (human epidermal growth factor receptor 2) is a protein found on the surface of cells that, when functioning normally, has been found to be a key component in regulating cell growth. However, when the HER2 protein is altered, extra HER2 protein receptors may be produced. This over-expression of HER2 causes increased cell growth and reproduction, often resulting in more aggressive breast cancer cells.

HER2 protein over-expression affects approximately 20% to 30% of breast cancer patients.

HER2 testing is currently performed on a sample of tissue that has been removed during cancer surgery. Testing may also be performed on cells from a breast tissue sample that has been stored from a previous surgery (many laboratories bank tissue samples for years after the initial biopsy or surgery).

Testing for HER2 protein over-expression involves applying a special staining solution to the tissue sample. The pathologist then examines the cells within the tissue sample, checking for stained areas which indicate where high levels of HER2 over-expression are present. Depending on the amount of stain uptake, the patient’s cancer may be classified as HER2 positive or HER2 negative.

Being tested for HER2 can be helpful because it functions as a prognostic indicator and can aid in treatment planning.  Those whose tumour is identified as HER2 positive may be eligible to receive a drug call Herceptin.