HER2-positive breast cancer

HER2-positive breast cancer is a subtype of early breast cancer. About 15-20% of people with early breast cancer have this subtype.

We explain what this subtype means.

About the HER2-positive subtype

‘HER2’ stands for human epidermal growth factor receptor 2. This is a protein that sits on the surface of the cancer cells and controls how healthy breast cells grow, divide and repair.

In HER2-positive breast cancer, the cancer cells have more HER2 protein ('receptors') on their surface than normal. When the HER2 gene isn’t working correctly, it makes too many copies of itself. The breast cancer cells grow and divide faster than they should. This is HER2 'over-expression'.

In a pathology report, breast cancers with HER2 protein over-expression are called HER2-positive.

HER2-positive breast cancers tend to grow faster than some other subtypes. However, very effective treatments are available.

Testing for HER2-positive breast cancer

After a diagnosis of early breast cancer, you will usually have a biopsy or surgery. During these procedures, tissue is removed for testing.

All breast cancers are tested to find out if they contain oestrogen receptors (ER), progesterone receptors (PRs and HER2.

Several tests can be done to find out if your breast cancer is HER2 positive or negative.

Immunohistochemistry (IHC) testing looks how many HER2 receptors are on the cancer cells. The result in your pathology report may be 0, 2+ or 3+. If it is 2+ or 3+, another test - in situ hybridisation (ISH) testing - is done. 

In situ hybridisation testing looks at specific genetic material (DNA or RNA) within cells to identify genetic changes.

This is often reported in the pathology report as ISH-amplified (positive) or ISH-non-amplified (negative).

• IHC 0: the cancer is HER2-negative
• IHC 1+, 2+, 3+ and ISH is negative (non-amplified): this is HER2-low breast cancer
• IHC 1+, 2+, 3+ and ISH is positive (amplified): this is HER2-positive breast cancer.

When HER2-positive breast cancer is also hormone receptor positive, it is referred to as triple positive breast cancer.