Some breast cancer cells have a higher than normal level of a protein called HER2 (human epidermal growth factor receptor 2) on their surface, which stimulates them to grow.
This is known as HER2 positive breast cancer.
Around one in five invasive breast cancers (breast cancer that has the potential to spread to other parts of the body) are HER2 positive.
How do I know if my breast cancer is HER2 positive or HER2 negative?
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 between one and three weeks later.
There are various tests to measure HER2 levels. 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. A score of 0 or 1+ means the breast cancer is HER2 negative. A score of 2+ is borderline and a score of 3+ means the breast cancer is HER2 positive.
Breast cancers with a borderline result (2+) should be retested using more specialised techniques to determine if they are truly HER2 positive or negative.
Treatment for HER2 positive breast cancer
If your breast cancer is HER2 positive, you’ll usually be offered a targeted (biological) therapy. These include: