Test result differences in HER2 status?

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Question from Mary: I was diagnosed with breast cancer a year ago. Initially on the needle biopsy path report, the HER2 result was "strongly positive." Then when the path report from the entire breast (post-mastectomy) came back, it said the tissue was HER2 negative. How could there be such a huge discrepancy in the two?
Answers - Marisa Weiss, M.D., President and Founder One cancer is usually made up of many different kinds of breast cells. We call this "tumor heterogeneity." It is possible that the sample removed initially did, in fact, have cancer that was HER2 positive and that the sample taken after treatment represented a different population within the cancer that was HER2 negative. The kind of difference in results that happen between samples is called the "sampling error."

It is also possible that you had HER2 positive cancer cells up front and that the treatment got rid of the HER2 positive cells, so that when the sample was taken after treatment, only the HER2 negative cells were left over. This is possible, but not necessarily likely.

Sometimes the results at one hospital or laboratory can differ from the results at another. That means testing is not identical at all places. Also, it's possible that two different kinds of tests were used to test for HER2. One test may have been a measure of HER2 protein levels ("IHC") and the other test could have looked at the HER2 gene level ("FISH"). Of these two tests, the FISH test is more reliable.

Try to work with your doctors to help sort this out so that your treatment moving forward is best tailored for your situation.

The Ask-the-Expert Online Conference called Your Operative and Pathology Reports featured Beth Baughman Dupree, M.D., F.A.C.S. and Ann Ainsworth, M.D. answering your questions about details of pathology and operative reports and the importance of discussing them with your doctors.

Editor's Note: This conference took place in November 2004.

The materials presented in these conferences do not necessarily reflect the views of Breastcancer.org. A qualified healthcare professional should be consulted before using any therapeutic product or regimen discussed. All readers should verify all information and data before employing any therapies described here.

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