Brightfield Double In Situ Hybridization Is Comparable to Fluorescence In Situ Hybridization for Determination of HER2 Amplification in Primary Gastric Adenocarcinoma
Andrea Grin, Christine Brezden-Masley, Sharon Bauer, Catherine J Streutker. St. Michael's Hospital, Toronto, Canada; University of Toronto, Toronto, Canada
Background: HER2 is increasingly being assessed in gastric cancer to identify patients that may benefit from trastuzumab therapy; patients with 3+ HER2 staining on immunohistochemistry (IHC) or amplification by in situ hybridization show a significant survival benefit. Fluorescence in situ hybridization (FISH) is traditionally used as the gold standard to evaluate HER2 amplification. This method is labour intensive, requires a skilled technologist, and specialized fluorescent microscopy. An alternative is the newly developed automated Brightfield Double in situ Hybridization (BDISH) technique and uses differentially labeled Chromosome 17 and HER2 probes that can be read by light microscopy. The aim of this study was to assess the utility of BDISH in gastric cancer and to compare the results to those obtained by IHC and FISH.
Design: Cases were identified from a gastric adenocarcinoma database. Formalin-fixed, paraffin-embedded primary gastric adenocarcinoma specimens were analyzed by IHC (4B5, Ventana), FISH (Abbott Molecular) and BDISH (Ventana). The correlation between methods was calculated.
Results: Results for 48 patients (75% intestinal, 15% diffuse, 10% mixed) were available for analysis. There was a 98% (47/48) concordance rate between BDISH and FISH results (see Table 1). The one discrepant case was scored as 2+ on IHC, was non-amplified by FISH (1.4), but showed amplification by BDISH (2.17). This case displayed tumor heterogeneity, resulting in variable CEP17:HER2 ratios by BDISH depending on the area counted. 71% (5/7) of 3+ cases by IHC were amplified by both BDISH and FISH. All amplified cases were of intestinal type. None of the 0+ or 1+ cases showed amplification by FISH or BDISH (0/31).
|IHC score||FISH amplified||FISH non-amplified||BDISH amplified||BDISH non-amplified||FISH BDISH concordance (%)|