Gwen’s best of SABCS 2011: Oncotype DX test underestimates HER2

by Gwen on January 8, 2012

© 2012 Carl H. Stritter All rights reserved.

You can find an overview of the most important presentations of the 2011 San Antonio Breast Cancer Symposium here.

Poster #01-07-20 by D. J. Dabbs and others

The Oncotype DX test is amazing. The folks at Genomic Health who developed it are my personal heroes. But recently a problem has cropped up. Genomic Health may not have fallen off their pedestal but they certainly have been teetering on the edge quite a bit lately.

The Oncotype DX test has been a godsend to those who want objective evidence of chemotherapy effectiveness before undergoing such a toxic regimen. Its scope has been recently expanded to quantifying ER (estrogen receptor) and PR (progesterone receptor) expression. This is served as a great “2nd opinion” on the pathology report since Oncotype ER and PR scores have been shown to predict response to anti-estrogen therapy.

Not so for the HER2 score. When a patient of mine had an Oncotype HER2 score much lower than FISH testing done at 2 other labs, I called Genomic Health. To my amazement, they admitted that they had not yet done the research to verify that their HER2 score accurately predicted who would and who would not benefit from trastuzumab (Herceptin). I asked them why they had no disclaimer on the HER2 score report – no answer was forthcoming.

One might theorize that the discrepancy lies not in the test, but in the tissue, where HER2 gene expression may differ from cell to cell. But if that were the case, one would expect Oncotype to sometimes overestimate and sometimes underestimate. But it turns out that it only underestimates. So I have ignored the HER2 score on the Oncotype DX report ever since.

This research report validates my approach. The authors found that Oncotype DX classified 71% of the HER2 FISH-positive and HER2 FISH-equivocal cases as HER2-negative. This is important since FISH-equivocal HER2 cancers respond just as well to trastuzumab treatment. A previous study by the same author looking at samples from 3 labs, including the Cleveland Clinic, found similar results.

Caveat: We need other independent researchers to validate this report by publishing their experience with the Oncotype DX HER2 score.

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*Information on the Breast Equity blog is provided on an “as is” basis for general information only. It is not intended as medical advice and should not be relied upon as a substitute for consultation with a qualified health professional.*

© 2012 Gwendolyn M Stritter, MD. All rights reserved.

© 2012, Gwen. All rights reserved.

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