HER2 positive breast cancer is cancer where the breast tumors have higher levels of a protein called human epidermal growth factor receptor 2 (HER2). The HER2 protein is a growth-promoting protein on the outside of all breast cells. HER2 positive breast cancer tends to grow and spread faster than other types of breast cancer and is in 1 out of 5 breast cancer cases. However, HER2+ breast cancer is likely to respond to targeted treatments for the HER2 protein.

Testing for HER2 Positive Breast Cancer

Patients newly diagnosed with breast cancer should be tested for HER2 because it can help determine which treatment option is best. This requires a biopsy of the tumor which is then tested with immunohistochemical stains (IHC) or Fluorescent in situ hybridization (FISH).

IHC, which is more common, is used to detect the presence of specific protein markers. FISH is a genetic mapping technique used to analyze chromosomal aberrations and genetic abnormalities.

If the IHC results are 0-1+, the breast cancer is HER2 negative.
If the IHC results are 3+, the breast cancer is HER positive.
If the IHC results are 2+, the breast cancer is called equivocal, and requires FISH testing to clarify HER2 positive or negative.

HER2 Positive Breast Cancer Treatment

HER2+ breast cancer can be treated with hormone drugs that target the HER2 protein. Typically, these types of treatments are effective, causing the prognosis for HER2+ breast cancer to be good. This is why understanding if breast cancer is HER2 positive or negative is important.

HER2+ breast cancer can also be treated with chemotherapy drugs, although this type of treatment doesn’t target the HER2 protein.

It’s recommended that all invasive breast cancer patients get testing for the levels of HER2 protein because it can strongly influence the treatment decisions.

Resources:

Breast Cancer HER2 Status | HER2+ Breast Cancer

HER2-positive breast cancer: What is it? – Mayo Clinic