Breast Cancer HER2 Status

Some women have breast tumors with higher levels of a protein known as HER2/neu – these are called HER2-positive breast cancers.

What is HER2/neu and what does it mean?

HER2/neu (often just shortened to 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. Women newly diagnosed with invasive breast cancers should be tested for HER2. It’s important to know  your “HER2 status” because HER2-positive cancers are much more likely to benefit from treatment with drugs that target the HER2 protein. Ask your doctor about your HER2 status and what it means for you.

How are breast tumors 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.

Many breast cancer specialists think that the FISH test is more accurate than IHC. However, it is more expensive and takes longer to get the results. Often the IHC test is done first.

  • If the result is 0 or 1+, the cancer is considered HER2-negative. They do not respond to treatment with drugs that target HER2.
  • If the result is 3+, the cancer is HER2-positive. They are usually treated with drugs that target HER2.
  • If the 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. These cancers are more common in younger women and in African-American or Hispanic/Latina women. Triple-negative breast cancers grow and spread more quickly than most other types of breast cancer. Because the cancer cells don’t have hormone receptors, hormone therapy is not helpful in treating these cancers. Because they don’t have too much HER2, drugs that target HER2 aren’t helpful, either. Chemotherapy can still be useful, though.

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.

American Society of Clinical Oncology. HER2 Testing for Breast Cancer. October 7, 2013. Accessed at on September 25, 2015.

Morrow M, Burstein HJ, Harris JR. Chapter 79: Malignant Tumors of the Breast. In: DeVita VT, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg’s Cancer: Principles and Practice of Oncology. 10th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2015.

National Comprehensive Cancer Network (NCCN). Practice Guidelines in Oncology: Breast Cancer. Version 2.2017. Accessed at on August 18, 2017.

Schott AF. Systemic treatment for HER2-positive metastatic breast cancer. Last updated Jun 07, 2017. Accessed August 18, 2017.

Wolff AC, Domchek SM, Davidson NE, Sacchini V, McCormick B. Chapter 91: Cancer of the Breast. In: Niederhuber JE, Armitage JO, Doroshow JH, Kastan MB, Tepper JE, eds. Abeloff’s Clinical Oncology. 5th ed. Philadelphia, Pa: Elsevier; 2014.

Last Medical Review: September 25, 2017 Last Revised: September 25, 2017

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