Determining sensitivity and specificity of HER2 testing in breast cancer using a tissue micro-array approach

Tim Ja Dekker,Gerrit Kj Hooijer,Sybren Lf Meijer,Susan Ter Borg,Joost Van Gorp,Marc J Van De Vijver,Jelle Wesseling,Wilma E Mesker,Vincent Thbm Smit,Judith R Kroep,Ed Schuuring,James E Boers,Jos Bart

doi:10.1186/bcr3208

Abstract

IntroductionOverexpression of the human epidermal growth factor receptor 2 (HER2) as a result of HER2 gene amplification is associated with a relatively poor prognosis in breast cancer and is predictive of HER2-targeting therapy response. False-positive rates of up to 20% for HER2 testing have been described. HER2-testing laboratories are therefore encouraged to participate in external quality control schemes in order to improve HER2-testing standardization.MethodsThis study investigated the feasibility of retesting large numbers of invasive breast cancers for HER2 status on tissue micro-array (TMA) as part of a quality control scheme. For this assessment different HER2 testing methods were used including HER2 detecting antibodies SP3, 4B5, Herceptest and mono color silver in situ hybridization (SISH) and dual color SISH. Final HER2 status for each tumor on the TMA was compared to the local testing result for the same tumor. Discordances between these two results were investigated further by staining whole tumor sections.ResultsFor this study, 1,210 invasive breast carcinomas of patients treated in six hospitals between 2006 and 2008 were evaluated. Results from the three immunohistochemistry (IHC) and two in situ hybridization (ISH) assays performed on the TMAs were compared. The final HER2 status on TMA was determined with SP3, 4B5 and mono color SISH. Concordance between local HER2 test results and TMA retesting was 98.0%. Discordant results between local and TMA retesting were found in 20 tumors (2.0%). False positive HER2 IHC results were identified in 13 (1.3%) tumors; false negative IHC results in seven (0.7%) tumors.ConclusionsRetesting large volumes of HER2 classified breast carcinomas was found to be feasible and can be reliably performed by staining TMAs with SP3, 4B5 and mono color SISH in combination with full-sized slides for discordant cases. The frequency of false-positive results was lower than previously reported in the literature. This method is now offered to other HER2-testing laboratories.

Highlights

Overexpression of the human epidermal growth factor receptor 2 (HER2) as a result of HER2 gene amplification is associated with a relatively poor prognosis in breast cancer and is predictive of HER2-targeting therapy response
HER2 amplified with dual color silver in situ hybridization (SISH) were scored as negative for amplification, eight tumors were scored equivocal for amplification and 11 tumors were again scored as HER2 amplified
At repeated assessment of mono color SISH results, two tumors that were initially scored as negative for amplification were scored as HER2 amplified and one tumor initially scored as positive was scored as HER2 negative

Summary

Introduction

Overexpression of the human epidermal growth factor receptor 2 (HER2) as a result of HER2 gene amplification is associated with a relatively poor prognosis in breast cancer and is predictive of HER2-targeting therapy response. HER2 status of primary breast cancer has been associated with relatively poor prognosis [3] and some studies have shown that HER2 positive tumors differ from HER2 negative tumors in their response to systemic hormonal therapy [4] and chemotherapy [5,6]. HER2 testing should be carried out in such a way that false positive and false negative test results are avoided in order to select the proper patients for HER2 targeted therapies

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Conclusion