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High False-Negative Rate for HER2 Status Using Oncotype DX

HER2 status in breast cancer with RT-PCR assay is discordant with IHC/FISH results

WEDNESDAY, Oct. 12 (HealthDay News) -- Genomic Health's (GHI) Oncotype DX test, a human epidermal growth factor receptor 2 (HER2) assay for breast cancer that uses a method of reverse transcription polymerase chain reaction (RT-PCR), has an unacceptable false-negative rate, according to a study published online Oct. 11 in the Journal of Clinical Oncology.

David J. Dabbs, M.D., from the Magee-Womens Hospital of the University of Pittsburgh Medical Center, and colleagues investigated the concordance rate between the GHI RT-PCR test and immunohistochemistry (IHC)/fluorescent in situ hybridization (FISH) assay of HER2 status. A total of 843 patients with available HER2 GHI RT-PCR assay results were included in the analysis from three participating institutions. All laboratories also conducted FISH analysis to classify their IHC-positive and equivocal cases.

The investigators found that IHC/FISH analysis classified 93 percent of cases as negative, 4 percent as positive, and 3 percent as equivocal. Of the IHC/FISH negative cases, 99 percent were also reported as negative by the GHI RT-PCR assay. All IHC/FISH equivocal cases were negative by the GHI RT-PCR assay. Of the IHC/FISH positive cases, 28, 33, and 39 percent were reported as positive, equivocal, and negative, respectively, by the GHI RT-PCR assay.

"There was an unacceptable false-negative rate for HER2 status with GHI HER2 assay in this independent study. This could create confusion in the decision-making process for targeted treatment and potentially lead to mismanagement of patients with breast cancer if only GHI HER2 information is used," the authors write.

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