Some breast cancer cells have a higher-than-normal level of a protein called HER2 on their surface, which stimulates them to grow. This is known as HER2-positive breast cancer.

1. What is HER2?

HER2 (human epidermal growth factor receptor 2) is a protein.

Some breast cancer cells have a higher than normal level of HER2 on their surface, which helps them to grow. This is known as HER2-positive breast cancer.

Less than 1 in 5 invasive breast cancers are HER2-positive.

If the cancer has normal levels of the HER2 protein it is called HER2-negative.

2. How do I know if my breast cancer is HER2-positive or HER2-negative?

Invasive breast cancer and HER2

All invasive breast cancers are tested for HER2 levels. This is done in a hospital laboratory on a sample of breast cancer tissue removed during a biopsy or surgery. The results are usually available within 1 to 3 weeks.

There are various tests to measure HER2 levels. A test called IHC (immunohistochemistry) is usually done first. It involves a special staining process performed on a sample of breast cancer tissue.

It’s reported as a score of 0–3:

  • 0 or 1+ means the breast cancer is HER2-negative
  • 2+ is borderline
  • 3+ means the breast cancer is HER2-positive

Breast cancers with a borderline result (2+) should be retested using more specialised techniques. These tests will give a result of HER2-positive, HER2-low or HER2-negative.


Ductal carcinoma in situ (DCIS) is not routinely tested for HER2 receptors.

Sometimes your pathology report may include HER2 results for DCIS. However, the HER2 levels will not affect your treatment options. This is because targeted therapies, such as trastuzumab, are not used to treat DCIS.

3. HER2 levels and treatment options


If your breast cancer is HER2-positive, you’ll usually be offered a targeted (biological) therapy alongside or after chemotherapy.

Targeted therapies you may be offered include:


There is some evidence that HER2-low breast cancer may benefit from targeted treatments, such as trastuzumab. However, more research is needed.

Targeted treatment for HER2-low breast cancer is not yet available outside of a clinical trial.

Speak to your treatment team for more information.


If your cancer is HER2-negative, targeted therapies will not be of any benefit to you.

If you have HER2-negative breast cancer, speak to your treatment team about the best treatment for you. Depending on the characteristics of your cancer and your general health, treatment options may include:

  • Surgery


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Quality assurance

This information was last reviewed in April 2023. The next planned review begins in April 2025.

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