Comparison of automated and manual FISH for evaluation of HER2 gene status on breast carcinoma core biopsies

BACKGROUND: Positive HER2 status identifies breast carcinomas that might respond to trastuzumab treatment. Manual HER2 fluorescent in situ hybridisation (FISH) is the most readily used method to detect HER2 gene amplification which defines positive HER2 status in addition to HER2 protein overexpression. Automation of HER2 FISH may improve HER2 gene testing. The aim of our study was to evaluate an automated HER2 FISH assay for assessing the HER2 genomic status. METHODS: Core biopsies of 100 invasive breast carcinomas were analysed in parallel using the PathVysion™ HER-2 DNA Probe Kit and the Leica HER2 FISH System for BOND™. To assess inter-method agreement, concordance analysis was performed for various numerical and categorical HER2/CEP17 FISH parameters. RESULTS: Carcinomas with all HER2 immunohistochemical scores were included (0+: 20; 1+: 20; 2+: 30; 3+: 30). Using either HER2/CEP17 ratio >2.2 or ≥2.0 as criterion for HER2 amplification, high levels of concordance were observed between automated and manual FISH (concordance rate 96%, κ coefficient 0.92). High levels of inter-method agreement were also found for HER2 copy number, CEP17 copy number, HER2/CEP17 ratio, the percentage of carcinoma cells with HER2/CEP17 ratio >2.2, and the presence of HER2 genetic heterogeneity, HER2 clusters and CEP17 polyploidy. CONCLUSIONS: HER2 testing using automated FISH is feasible on breast carcinoma core biopsies. Automated HER2 FISH using the Leica HER2 FISH System for BOND is a practical and efficient alternative to manual HER2 FISH in evaluating the HER2 status of primary invasive breast carcinomas.