P5-11-15: Should HER-2 Score 0/1+ Breast Cancer Cases Be Retested by In-Situ Hybridisation? Results of a Multicenter Retesting Study.

Abstract

Abstract Background: HER-2 status is vital for selection of appropriate therapy for breast cancer patients. Accuracy of immunohistochemistry (IHC) varies with a major problem of false negative testing. To assess the false negative rate retesting by in situ hybridisation was performed on a group of primary breast cancers in which according to guidelines routine retesting is not recommended. Material and Methods: 570 breast cancers from 5 pathology departments scored 0/1+ by IHC (HercepTest or 4B5-antibody) were retested by HER2−Dual-SISH (BDISH) in a central laboratory. CAP/ASCO guidelines were applied. Cases showing ratios in the amplified or equivocal range by BDISH were further analysed by fluorescence in situ hybridisation (FISH) using Pathvysion® and ZytoLight® and retested centrally by IHC using 4B5 antibody (Ventana). Results: 25/570 cases (4.38%) were amplified by BDISH, the majority with low level amplification (ratios ≤ 3.26). Only two cases showed high level ratios (6.35 and 6.48). 17/570 cases (2.98%) showed ratios by BDISH in the equivocal range (1.8 — 2.2). 24 amplified and 17 equivocal cases underwent further retesting. In one case no tumor tissue was available for further testing. On further testing 17/24 (71%) BDISH-amplified cases showed IHC scores 2+/3+ and 7/24 (29%) cases showed IHC scores 0/1+. Subsequently 3/13 score 2+ cases were amplified by Pathvysion® and 9/13 by ZytoLight®. 3/4 score 3+ cases were amplified by both FISH assays. In case of amplification ratios of BDISH and both FISH assays appeared to be in the same range. Only 2/17 BDISH-equivocal carcinomas were confirmed equivocal by Pathvysion® and 6/17 were confirmed equivocal by ZytoLight®. All other BDISH-equivocal cases were non-amplified by both FISH assays. Discrepant results between different methods could partly be caused by interobserver variability. This question is currently under investigation. Overall, after multistep retesting amplification occurred in only 17 cases (2.98%). Discussion: Amplification is rare in immunohistochemically HER-2 negative breast carcinomas and occurred predominantly at low level in our study. Low level amplification seemed to be diagnosed more frequently by BDISH compared with FISH. Since clinical data demonstrate a benefit of therapy even in carcinomas with low level amplification the identification of these carcinomas might be of interest. Conflicts of Interest: The study was supported by Roche Austria GmbH. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-11-15.