HER2 Positive Breast Cancer

Author: Marisa Healy, BSN, RN
Last Reviewed: November 18, 2022

HER2 stands for human epidermal growth factor receptor 2. HER2 is a gene that makes HER2 proteins, which are receptors on breast cells. These receptors are found in normal breast tissue. They control how breast tissue grows and repairs itself.

In some cases, there are too many HER2 receptors. This is called over-expression. These extra HER2 receptors cause breast cells to grow more quickly and out of control, forming a tumor. HER2 positive (HER2+) breast cancers tend to grow quickly and may recur (come back) more often. About 1 out of every 5 (10-20%) breast cancers are HER2+. HER2+ breast cancer can also be hormone receptor (HR) positive.

How do I know if my cancer has too much HER2?

After a breast biopsy or surgery, a sample of the tumor is tested for extra HER2. This result can be found in your pathology report. There are two tests for HER2: the immunohistochemistry (IHC) test and the FISH test (fluorescent in situ hybridization). The results of these 2 tests are reported differently.

  • The immunohistochemistry (IHC) test looks for overexpression of the HER2 protein. The result is reported as a number from 0 to +3.
    • Zero and +1 are considered Her 2 negative.
    • +2 is borderline and +3 is considered Her 2 positive.
  • The FISH test (fluorescent in situ hybridization), checks the tumor for extra copies of the Her 2 gene. The result is reported as positive or negative.

IHC is faster and costs less money, so it is often the first test done. Patients with a +2 (borderline) result on IHC should have the FISH test done to see if the borderline result is positive or negative.

If your breast cancer recurs, talk with your provider about re-testing your tumor. Research has shown that HER2 status can change over time. This means if you are HER2 negative, your tumor could become HER2 positive; if your tumor is HER2 negative it could become HER2 positive.

How are HER2 positive breast cancers treated?

Once your provider knows that your cancer is HER2 positive, they can use “targeted therapy.” Targeted therapy uses medications that target genes and proteins on cancer cells. This slows down or kills the cancer cells while keeping your healthy cells as safe as possible. The targeted therapy medication attaches to HER2 receptors on the surface of breast cancer cells. This blocks the receptors from receiving signals to grow. By blocking the signals, the tumor growth can be slowed or stopped.

How can I manage this diagnosis?

  • While the diagnosis of breast cancer may be hard, remember there are many treatment options.
  • Learn about your type of breast cancer and common treatments. This can help you ask questions at your visits and feel more in control of your treatment decisions.
  • Seek out support groups or peer support (online or by phone).
  • All cancers are unique, and you should not compare your experience to others.


OncoLink's Resources for More Information: Breast Cancer.

Godone, R. L. N., Leitão, G. M., Araújo, N. B., Castelletti, C. H. M., Lima-Filho, J. L., & Martins, D. B. G. (2018). Clinical and molecular aspects of breast cancer: Targets and therapies. Biomedicine & Pharmacotherapy, 106, 14-34.

Loibl, S., & Gianni, L. (2017). HER2-positive breast cancer. The Lancet, 389(10087), 2415-2429.

Pondé, N., Brandão, M., El-Hachem, G., Werbrouck, E., & Piccart, M. (2018). Treatment of advanced HER2-positive breast cancer: 2018 and beyond. Cancer treatment reviews, 67, 10-20.

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