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HER2 status test

HER2 is the more common name for the gene called ERBB2. HER2 (or HER2/neu) stands for human epidermal growth factor receptor 2. The job of HER2 is to control a protein on the surface of cells that helps them grow. If the HER2 gene changes, it may help a tumour grow.

Healthy cells have 2 copies of the HER2 gene. When there are too many copies of the HER2 gene in a cell, this leads to too much HER2 protein being made. Having too many copies of the gene is called amplification, and having too much HER2 protein being made is called overexpression of HER2.

Why the HER2 status test is done

HER2 status testing is done to find out how much HER2 a tumour makes. Knowing this helps your healthcare team plan your treatment.

HER2 status testing for breast cancer is done on the main, or primary, breast tumour at the time of diagnosis, along with hormone receptor status testing. Breast cancer is the most common type tested. Because HER2 status can sometimes change over time, or with treatment, testing may be done again if the breast cancer comes back or spreads to another part of the body (metastasizes).

HER2 status testing is also done with advanced stomach cancers. In some Canadian cancer centers it is done for advanced cancers that are in the area where the esophagus joins the stomach (called the gastroesophageal, or GE junction).

Research studies show that other types of cancer, such as ovarian, bladder and lung, may also overexpress HER2. More research is needed to understand the role that HER2 overexpression may have with these tumours. Testing for HER2 in cancers other than breast, stomach and the GE junction is not available in Canada except as part of a clinical trial.

How the HER2 status test is done

HER2 status testing is done on a biopsy sample taken from the tumour. There are 2 ways to test HER2 status.

Immunohistochemistry (IHC) measures the amount of HER2 protein in the cancer cells.

Fluorescence in situ hybridization (FISH) looks at the number of copies of the HER2 gene in the cancer cells.

If the test results aren’t clear with one test, the other may be used to get a more definite result.

There is also a HER2 blood test, but it’s not used to find out if a tumour is HER2 positive. The HER2 blood test may be used to monitor how treatment is working in women with HER2 positive metastatic breast cancer whose levels of HER2 were high (greater than 15 ng/mL) before they started treatment. Using the HER2 blood test to monitor women with low blood levels of HER2 is not useful.

What the results mean

With IHC testing, the results are reported on a scale from 0 to 3+.

ScaleMeaning

0 or 1+

The HER2 level is normal.

The tumour is HER2 negative.

2+

There is some overexpression of HER2.

A FISH test will be done to confirm the HER2 status.

3+

The HER2 is higher than normal.

The tumour is HER2 positive.

FISH test results are reported as either negative or positive.

FISH negative means that the levels of the HER2 gene in the cells are normal, and the tumour is HER2 negative.

FISH positive means that there is at least 4 copies of the HER2 gene in the cells, and the tumour is HER2 positive.

HER2-positive cancers are more aggressive, which means that they tend to grow and spread more quickly than cancers with a normal amount of HER2. HER2-positive tumours usually have a higher tumour grade.

What happens if HER2 overexpression is found

If you have a HER2-positive cancer, you may be offered treatment with a drug called trastuzumab (Herceptin). Trastuzumab is designed to attach to the extra HER2 proteins, which stops the growth of the cancer.

If both the IHC and the FISH tests are positive, trastuzumab is more likely to slow or halt the growth of the tumour. If the IHC is negative but the FISH is positive, the cancer may still respond to the drug.

Trastuzumab does not help people with HER2-negative cancer.

Breast cancer, advanced stomach cancer and advanced cancer of the GE junction are treated with trastuzumab in Canada right now. Clinical trials are looking at the use of trastuzumab with other cancers.

For more detailed information on trastuzumab, go to sources of drug information.

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