Breast Cancer HER2 Status

Some women have breast tumors with higher levels of a protein known as HER2 – these are called HER2-positive breast cancers. Ask your doctor about your HER2 status and what it means for you.

What is HER2 and what does it mean?

HER2 is a growth-promoting protein on the outside of all breast cells. Breast cancer cells with higher than normal levels of HER2 are called HER2-positive. These cancers tend to grow and spread faster than other breast cancers, but are much more likely to respond to treatment with drugs that target the HER2 protein.

How are breast tumors tested for HER2?

Women newly diagnosed with invasive breast cancers should be tested for HER2. 

A biopsy or surgery sample of the cancer is usually tested with either immunohistochemical stains (IHC) or Fluorescent in situ hybridization (FISH).

See Testing Biopsy and Cytology Specimens for Cancer and Understanding Your Pathology Report: Breast Cancer to get more details about these tests.  

What do the test results mean?

The results of HER2 testing will guide you and your cancer care team in making the best treatment decisions.

It is not clear if one test is more accurate than the other, but FISH is more expensive and takes longer to get the results. Often the IHC test is done first.

  • If the IHC result is 0 or 1+, the cancer is considered HER2-negative. These cancers do not respond to treatment with drugs that target HER2.
  • If the IHC result is 3+, the cancer is HER2-positive. These cancers are usually treated with drugs that target HER2.
  • If the IHC result is 2+, the HER2 status of the tumor is not clear and is called "equivocal." This means that the HER2 status needs to be tested with FISH to clarify the result.

Triple-negative breast tumors don’t have too much HER2 and also don’t have estrogen or progesterone receptors. They are HER2-, ER-, and PR-negative. Hormone therapy and drugs that target HER2 are not helpful in treating these cancers. See Triple-negative Breast Cancer to learn more.

Triple-positive breast tumors are HER2-, ER-, and PR-positive. These cancers are treated with hormone drugs as well as drugs that target HER2.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Henry NL, Shah PD, Haider I, Freer PE, Jagsi R, Sabel MS. Chapter 88: Cancer of the Breast. In: Niederhuber JE, Armitage JO, Doroshow JH, Kastan MB, Tepper JE, eds. Abeloff’s Clinical Oncology. 6th ed. Philadelphia, Pa: Elsevier; 2020.

Jagsi R, King TA, Lehman C, Morrow M, Harris JR, Burstein HJ. Chapter 79: Malignant Tumors of the Breast. In: DeVita VT, Lawrence TS, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg’s Cancer: Principles and Practice of Oncology. 11th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2019.

National Comprehensive Cancer Network (NCCN). Practice Guidelines in Oncology: Breast Cancer. Version 2.2019. Accessed at https://www.nccn.org/professionals/physician_gls/pdf/breast.pdf on July 31, 2019.

Yamauchi H and Hayes DF. HER2 and predicting response to therapy in breast cancer. UpToDate website. https://www.uptodate.com/contents/her2-and-predicting-response-to-therapy-in-breast-cancer. Last updated Sept 05, 2018. Accessed July 31, 2019.

Wolff AC, Hammond MEH, Allison KH, Harvey BE, Mangu PB, Bartlett JMS et al. Human Epidermal Growth Factor Receptor 2 Testing in Breast Cancer: American Society of Clinical Oncology/College of American Pathologists Clinical Practice Guideline Focused Update. J Clin Oncol. 2018;36(20):2105-2122.

Last Medical Review: September 20, 2019 Last Revised: September 20, 2019

American Cancer Society medical information is copyrighted material. For reprint requests, please see our Content Usage Policy.