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This page is about HER2 and breast cancer. HER2 is a protein that can affect the growth of cancer cells. This information should ideally be read with our information about breast cancer| and also about trastuzumab (Herceptin®)|.
HER2 is a protein found on the surface of certain cancer cells. Some breast cancers have a lot more HER2 receptors than others. In this case, the tumour is described as being HER2-positive. Tumours that are HER2-positive tend to grow more quickly than other types of breast cancer. Knowing if a cancer is HER2-positive can sometimes affect the choice of treatment. Women with HER2-positive breast cancer can benefit from a drug called trastuzumab (Herceptin®). Herceptin only works in people who have high levels of the HER2 protein.
Your specialist should be able to tell you if you have HER2-positive breast cancer and if Herceptin may be helpful to you.
To understand HER2, it first helps to know a little about receptors and growth factors:
HER2 is a receptor found on the surface of certain cancer cells. It is made by a specific gene called the HER2/neu gene. HER2 is a receptor for a particular growth factor called human epidermal growth factor, which occurs naturally in the body. When human epidermal growth factor attaches itself to HER2 receptors on breast cancer cells, it can stimulate the cells to divide and grow.
Some breast cancer cells have a lot more HER2 receptors than others. In this case, the tumour is described as being HER2-positive. It is thought that about 1 in 5 women with breast cancer will have HER2-positive tumours.
Tests can be done to find out whether a woman has HER2-positive breast cancer. Testing will usually be done at the same time as the initial biopsy or breast cancer surgery. Samples of cancer tissue from previous biopsies or an earlier surgery also may be used if you have not already been tested.
The Department of Health announced in October 2005 that all newly diagnosed women with breast cancer will be tested for HER2. Women who have already been treated for breast cancer can be tested for HER2 if their cancer should ever come back.
If you are wondering about the relevance of HER2 testing in your situation, it may be helpful to discuss this with your specialist.
The two main methods used for HER2 testing are immunohistochemistry (IHC) and fluorescence in-situ hybridization (FISH):
Immunohistochemistry (IHC) can show how much of the HER2 protein is present in the tumour sample. The HER2 level is graded from 0 to 3+.
When a tumour is scored at 2+, UK testing guidelines recommend that a further test is carried out. This is because a result of 2+ does not always mean a cancer cell has a high level of HER2. In this situation, an extra test (FISH) is used to give a definite result.
Whereas IHC measures the level of HER2 protein in the tumour sample, FISH testing measures the amount of the HER2/neu gene in each cell. This gene is responsible for the overproduction of the HER2 protein.
There is no number scale for FISH testing. The result is either:
Hormonal therapies are most effective in women whose cancer cells have receptors for oestrogen and/or progesterone. They are referred to as being oestrogen or progesterone receptor positive|. There are many different types of hormonal therapy, and they all work in slightly different ways.
It has been suggested that a woman’s HER2 status might influence which hormonal therapy may be effective for her. However, more research is needed in order to reach firm conclusions.
For more on HER2-positive breast cancer, and to find out if Herceptin is right for you, please see our section on Herceptin|.
This section has been compiled using information from a number of reliable sources, including:
Content last reviewed: 1 December 2010
Next planned review: 2012
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