Wednesday, April 21, 2010
Recent media coverage on HER2 testing for breast cancer might generate questions from patients. HER2-positive breast cancer is a breast cancer that tests positive for a protein called human epidermal growth factor receptor 2 (HER2), which promotes the growth of cancer cells. In about 1 of every 5 breast cancers, the cancer cells make an excess of HER2 due to a gene mutation. This gene mutation and the elevated levels of HER2 that it causes can occur in many types of cancer — not only breast cancer. HER2-positive breast cancers tend to be more aggressive than other types of breast cancer. The following Q & A has been developed to answer some commonly asked questions.
Q. I don't understand what these tests are all about...
A. Researchers have made significant progress in understanding the molecular basis of breast cancer in the past decades — more so than for some other cancers — and as a result, we have a good (and growing) arsenal of targeted therapies to offer patients. The tests analyze specific molecules that are found on cancer cells, which can then be matched to a treatment for that particular class of cancer. For example, 15-20 percent of breast cancer patients are affected by HER2+ breast cancer, which is driven by overactive HER2 growth — promoting genes or by excess HER2 protein. Several different tests exist to diagnose this tumor condition, and drugs such as Herceptin are available to reduce the activity of these proteins.
Q. Are there problems with the tests that my breast cancer therapy is based on?
A. If you are a Mayo Clinic patient, the administration and the analysis of your test, and the clinical decisions made from the results, are amongst the best that any institution can offer. Researchers at Mayo Clinic are in the forefront of identifying issues in these tests on a national basis, and conducting studies to improve patient identification for therapies and outcomes. Mayo Clinic has one of the largest central laboratories in the United States that analyze these tests; these central laboratories have state-of-the art expertise and strict quality assurance programs.
We feel it is necessary to help develop and agree on national guidelines that will standardize use and evaluation of these tests, both at central laboratories and at smaller laboratories that only occasionally handle these tests.
Q. How do I know where my test was read?
A. If you are a Mayo Clinic breast cancer patient, your test was analyzed at our central laboratory (see above).
Q. I was told I have HER2+ breast cancer, but I am not responding to Herceptin. Does that mean my test results were in error?
A. Even if the tumors are HER2-positive, that does not mean that all patients will respond to Herceptin — although the HER2 test can be used to exclude patients for this type of anti-HER2 therapy. In other words, data suggest that Herceptin is not indicated unless the tumor has been found to be HER2-positive. Our goal is to understand more about these tumors in order to improve the predictive power of these tests — and, thus, improve the care we give to our patients.
Q. Are there similar problems with tests that analyze whether tumors respond to estrogen- the so-called ER/PR tests?
A. Although these tests have been available for a long time, further refining is also under evaluation, and new national guidelines for quality assurance are in development. Again, we at Mayo have a significant amount of experience with these tests and we follow all developments in the field.
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