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. HER2-positive breast cancers tend to grow and spread faster than other breast cancers. Finding out the HER2 status of your breast tumor is important because there are treatments targeted at 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, such as trastuzumab (Herceptin®). 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 one of the following:

  • Immunohistochemical stains (IHC): In this test, special markers are used that identify the HER2 protein. If many copies of HER2 are present, the cells will change color. This color change can be seen under a microscope.
  • Fluorescent in situ hybridization (FISH): This test uses fluorescent pieces of DNA that stick to copies of the HER2/neu gene inside the cells, which can then be counted under a special microscope. (The HER2/neu gene makes the HER2 protein.)
  • A newer type of test, known as chromogenic in situ hybridization (CISH), works much like FISH, by using small DNA probes to count the number of HER2/neu genes in breast cancer cells. But this test looks for color changes (not fluorescence) and doesn't require a special microscope. This may make it less expensive. But right now it’s not being used as much as IHC or FISH.

Read about testing biopsy and cytology specimens for 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 is done first. The results come back as 0, 1+, 2+, or 3+.

  • If the results are 0 or 1+, the cancer is HER2-negative.
  • When the IHC result is 2+, the HER2 status of the tumor is not clear. This usually leads to retesting with FISH. FISH results come back as positive or negative for excess HER2.
  • If the test comes back 3+, the cancer is HER2-positive. But sometimes the FISH test is used to confirm HER2 status that is found to be 3+ by an IHC test.

HER2-positive breast tumors have too much HER2 protein or extra copies of the HER2 gene. They can and should be treated with drugs that target HER2. 

HER2-negative breast tumors don’t have excess HER2. They do not respond to treatment with drugs that target HER2.

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 tend to be found 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.

Questions to ask your doctor about HER2

These are some questions that would be good to have on hand when talking to your doctor about your breast cancer test results:

  • Has my tumor been tested for HER2?
  • What’s my HER2 status?
  • Was the test clear or should another test be done?
  • How does my HER2 status affect my treatment plan?

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared 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.

Last Medical Review: June 1, 2016 Last Revised: August 18, 2016

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