The clinical utility of ERBB2 amplification detection in breast carcinoma using a 341 gene hybrid capture-based next generation sequencing (NGS) assay: Comparison with standard immunohistochemistry (IHC) and Fluorescence In Situ Hybridization (FISH) assays.

604 Background: Approximately 15-20% of invasive breast carcinomas (BCA) show HER2/ERBB2 gene amplification which determines eligibility for treatment by targeted therapy. Traditionally, HER2 status is determined by IHC and FISH. NGS methods can be used to assess HER2 status in clinical practice but concordance with IHC/FISH is not well established. We report our experience using NGS for the assessment of HER2 amplification in conjunction with the detection of potentially targetable mutations. Methods: BCA samples ( > 10% tumor) were analyzed in a CLIA-certified lab using a hybrid capture-based NGS assay (“MSK-IMPACT”) designed to detect somatic genetic alterations in 341 genes, including copy number alterations. Tumor percentage and concurrent IHC/FISH results were recorded (using ASCO/CAP 2013 guidelines). Criteria for amplification by NGS were defined as a fold change (FC) ≥ 2, p-value < 0.05. Results: A total of 133 BCA samples (63 primaries, 70 mets) were analyzed. Compared to the combined IHC/FISH m...