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Breast Cancer HER2 Status
About 15% to 20% of breast tumors have higher levels of a protein known as HER2. These cancers are called HER2-positive breast cancers. Ask your cancer care team about your HER2 status and what it means for you.
What is HER2 and what does it mean?
HER2 is a protein that helps breast cancer cells grow quickly. Breast cancer cells with higher than normal levels of HER2 are called HER2-positive. These cancers tend to grow and spread faster than breast cancers that are HER2-negative, but are much more likely to respond to treatment with drugs that target the HER2 protein.
All invasive breast cancers should be tested for HER2 either on the biopsy sample or when the tumor is removed with surgery.
How are breast tumors tested for HER2?
Either a test called an immunohistochemistry (IHC) test or fluorescence in situ hybridization (FISH) test is used to find out if cancer cells have a high level of the HER2 protein.
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.
Often the IHC test for HER2 is done first. This is commonly followed by the FISH test to further classify the tumor type.
- If the IHC result is 0 with no membrane staining, the cancer is considered HER2-negative. These cancers do not respond to treatment with drugs that target HER2.
- If the IHC result is 0 with membrane staining (HER2+ staining in more than 0% but no more than 10% of tumor cells), the cancer is considered HER2-ultralow. These cancers may respond to certain drugs called antibody-drug conjugates.
- If the IHC is 1+ OR if the IHC is 2+ but FISH is negative, the cancer is considered HER2-low. These cancers may respond to certain drugs called antibody-drug conjugates.
- If the IHC is 2+ and the FISH is positive OR IHC is 3+, the cancer is HER2-positive. These cancers are usually treated with drugs that target HER2.
Triple-negative breast cancers 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 cancers are HER2-positive, ER-positive, and PR-positive. These cancers are treated with hormone drugs as well as drugs that target HER2.
- Written by
- References
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 editors and translators with extensive experience in medical writing.
Franchina M, Pizzimenti C, Fiorentino V, Martini M, Ricciardi GRR, Silvestris N, Ieni A, Tuccari G. Low and Ultra-Low HER2 in Human Breast Cancer: An Effort to Define New Neoplastic Subtypes. Int J Mol Sci. 2023 Aug 14;24(16):12795. doi: 10.3390/ijms241612795. PMID: 37628975; PMCID: PMC10454084.
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 7.2021 – August 23, 2021. Accessed at https://www.nccn.org/professionals/physician_gls/pdf/breast.pdf on August 31, 2021.
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 Revised: January 29, 2025
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