[2051] The Ventana INFORM HER2 Dual In Situ Hybridization (DISH) DNA Probe Cocktail Assay Versus Fluorescence In Situ Hybridization (FISH): Focussed Study of Immunohistochemical 2+ Cases

Faye F Gao, David J Dabbs, Rohit Bhargava. Magee-Womens Hospital of University of Pittsburgh Medical Center, Pittsburgh, PA

Background: The Ventana INFORM HER2 Dual in-situ hybridization (DISH) DNA probe cocktail assay is a new FDA approved technique designed to determine HER2 gene status by using light microscopy. We compared this new methodology with standard fluorescence in situ hybridization (FISH) on the most challenging group of breast cancers, i.e. HER2 immunohistochemical (IHC) 2+ cases.
Design: This prospective validation study was performed on 104 invasive breast cancer cases with equivocal HER2 IHC results (IHC score 2+). Both FISH and DISH were performed on the same tumor blocks. The DISH assay staining results were enumerated by counting at least 20 nuclei by an experienced pathologist blinded to FISH results. Similar to FISH, areas with stronger IHC staining were counted in heterogeneous cases. For both FISH and DISH, HER2 amplification was defined as HER2/Chr17 ratio 2.0. Cases with HER2/Chr17 ratio <2.0 were considered as non-amplified. In addition, 20 HER2 IHC 3+ invasive carcinoma cases (represented on a tissue microarray) were also evaluated by DISH.
Results: DISH was successful in 96 of 104 cases (92%) in the first attempt. Of the 8 cases that failed the first time, 7 cases showed optimal signals on repeat DISH, with overall success rate of 99% with 2 attempts. The overall concordance between FISH and DISH was 92% for these IHC 2+ cases (see table). Four cases were amplified by FISH and not amplified by DISH. The HER2 to Chr17 ratio on these 4 cases by FISH ranged from 2.04 to 2.06. Four cases were amplified by DISH and not amplified by FISH. The HER2 to Chr17 ratio on these 4 cases by DISH ranged from 2.08 to 2.58. All 20 (100%) IHC 3+ cases showed clusters of HER2 gene consistent with HER2 amplification by DISH.

 DISH AmplifiedDISH Not AmplifiedTotal
FISH Amplified7411
FISH Not Amplified48892
1 case failed by DISH in 2 attempts.

Conclusions: The Ventana INFORM HER-2 DISH assay shows excellent concordance with FISH assay for these most challenging (IHC 2+) breast cancer cases. Even for discordant cases, the HER2:Chr17 ratios remain within margin of error for either (FISH or DISH) assays. The presence of HER2 amplification in 100% of IHC 3+ cases suggests that false negative rate for DISH is close to negligible. DISH is performed under bright-field microscopy where the tissue morphology is better appreciated and additionally it is less expensive and faster than FISH. Our study provides strong evidence for replacing FISH with DISH assay.
Category: Techniques

Monday, March 4, 2013 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 306, Monday Morning


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