Invasive breast cancer clinical outcome is predicted by a novel bright-field assay for the simultaneous detection of HER2 gene amplification and protein expression (SILVERFISH)

Abstract

667 Background: A bright-field assay, SILVERFISH, simultaneously detects HER2 gene copy and protein expression, We analyzed the accuracy of SILVERFISH in predicting clinical outcome and assessed its concordance with FISH and IHC. Methods: Tissue microarrays from 444 invasive breast carcinomas were evaluated with SILVERFISH which includes enzyme metallography (EnzMetTM, Nanoprobes) for HER2 gene amplification (Am J Pathol. 160:1589–1595;2002), and IHC with CB11 for IHC detection of HER2 protein. Gene amplification was scored qualitatively (amplified vs.non-amplified) and CB11 staining was scored on a 0 to 3+ scale, and correlated with clinical outcomes by Kaplan-Meier survival analysis (log-rank). Results were correlated with FISH (Vysis) and IHC (DAKO) using kappa statistics. Results: SILVERFISH detected HER2 gene amplification in 108 of 444 (24%) tumors. Simultaneous protein overexpression (2+/3+) was identified in 71 (65%) cases, and 37 (34%) of the HER2-amplified cases were IHC negative. 6 of 336 (1%) HER2 non-amplified cases were IHC 2+/3+; 330 were 0 or 1+. SILVERFISH HER2 gene copy and protein status correlated with amplification by FISH (Kappa=.79) and IHC (Kappa=.71). HER2 status defined by either components of SILVERFISH predict survival and correlate with clinical outcome (p=0.02 for gene amplification, p=0.002 for protein overexpression). Conclusion: HER2 status as determined by SILVERFISH has good concordance with FISH and IHC, and correlates with clinical outcome. The simultaneous visualization of HER2 gene signal and protein allows for a practical and complete assessment of HER2 status. Supported in part by NIH SBIR CA83618. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Nanoprobes; Ventana Medical Systems Ventana Ventana Ventana Medical Systems International Ventana Medical Systems International