Abstract 334: Comparison of an in situ hybridization technique based on fluorescence (FISH) with dual color silver-enhanced ISH (SISH) for the validation of equivocal (borderline) status of HER2 (erbb2) in invasive breast carcinoma

Abstract

Abstract Aims: Accurate determination of HER2 gene amplification is necessary for the selection of patients for trastuzumab therapy. FISH is regarded as the gold standard method for detecting HER2 gene amplification. In comparison to FISH, SISH has the advantages of being a method evaluated by bright-field microscopy and generating stable signals. Several studies have shown an excellent concordance between different ISH methods in detection of clearly HER2 amplified and non-amplified breast carcinomas. Aim of this study is to compare the performance of dual color SISH (dSISH) in breast carcinoma with equivocal HER2 status with conventional FISH analysis. Material&Methods: From two different Institutes, biopsies from 62 female patients with invasive breast carcinoma were investigated independently for HER2 with FISH, single color SISH (sSISH) and the dSISH technique. FDA-approved FISH method was used. HER2 gene and CEN17 signals were counted separately. The strength of linear correlation of HER2/CEN17 measurements between FISH and sSISH and between sSISH and dSISH was evaluated and agreement assessed using Bland-Altman plots, which describe the average HER2/CEN17 of the two methods versus the difference between both methods. Concordance of HER2/CEN17 assessed by FISH and dSISH for ratios of 1.5-1.8, 1.8-2.0, 2.0-2.2 and 2.2-2.5 (called categories) were determined using the weighted kappa statistic. Results: For FISH and sSISH, the correlation of HER2/CEN17 between both methods was 0.61 and considerably improved when comparing sSISH versus dSISH (correlation coefficient: 0.79). Compared to FISH, dSISH tended to over-estimate HER2/CEN17 by 0.42 signals on average, whereas 95% of all differences between FISH and dSISH ranged within a ratio of 2.4. In tumors with equivocal FISH-HER2 status (ratio 1.8-2.0 and 2.0-2.2) dSISH was highly discrepant with concordance only of 11.1% and 42.9%, respectively. In 22.2% and 28.6% of these cases dSISH results in HER2 amplification. Concordance between FISH and dSISH was greatest for HER2/C17 ratios of 1.5-1.8 and 2.2-2.5, yet kappa values still demonstrated only fair agreement (κ=0.30 and κ=0.33). Conclusion: In comparison to FISH, ISH methods like SISH have the advantage of generating stable signals and can be evaluated by bright-field microscopy. Fair agreement was achieved with dSISH when HER2/CEN17 ratio was between 1.5-1.8 and 2.2-2.5 respectively by FISH. Breast carcinoma with equivocal status for HER2 in FISH analysis was poorly reproducible with dSISH with concordance of 54% of the cases. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 334.