A UK NEQAS ISH multicenter ring study using the Ventana HER2 dual-color ISH assay.

We performed a multicenter assessment of a new HER2 dual-color chromogenic in situ hybridization (CISH) test and herein report on concordance of CISH data with fluorescence in situ hybridization (FISH) data and intraobserver and interlaboratory scoring consistency. HER2 results were evaluated using duplicate cores from 30 breast cancers in 5 laboratories using the Ventana HER2 dual-color ISH assay (Ventana Medical Systems, Cambridgeshire, England) and in 1 central laboratory using a standard FISH assay. Overall 93.3% of cases were successfully analyzed by CISH across the 5 participating laboratories. There was excellent concordance (98.0% overall) for diagnosis of HER2 amplification by CISH compared with FISH. Intraobserver variability (7.7%) and intersite variability (9.1%) of absolute HER2/chromosome enumeration probe 17 ratios were tightly controlled across all participating laboratories. The Ventana HER2 dual-color ISH assay is robust and reproducible, shows good concordance with a standard FISH assay, and complies with requirements in national and international guidelines for performance of ISH-based diagnostic tests.