Comparison of Dual-ISH (DISH) With Fluorescence In Situ Hybridization (FISH) and Correlation With Immunohistochemical Findings for HER2/Neu Status in Breast Carcinoma.

Abstract

The most widely used methods for determination of HER2/neu status in breast carcinoma are immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH). Both techniques are associated with technical and interpretive difficulties. Alternative methods exist including quantitative PCR and the newly developed chromogenic dual in situ hybridization (DISH). We evaluated HER2 DISH as an alternative to FISH and report our findings from 101 cases. In addition, we correlated HER2 DISH and FISH results with HercepTest and 4B5 immunohistochemistry. Eight cases failed FISH analysis and none failed DISH analysis. A 95% (88/93) concordance was found between DISH and FISH for all cases in the series. When only 2+ IHC cases were evaluated, the concordance was 94% for DISH and FISH. Using the 2013 ASCO/CAP recommendations, none of the tested cases were equivocal by FISH or DISH despite 66% of cases being 2+ by HercepTest and 32% by the 4B5 antibody. Our study, which utilizes a majority of IHC equivocal cases, demonstrates that HER2 FISH and DISH are concordant methodologies. HER2 DISH is therefore an acceptable alternative to FISH.