New brightfield in-situ hybridization (BRISH) methods based on the cohybridization of probes to the HER2 gene and chromosome 17 centromere have been developed and provide a promising alternative to fluorescence in-situ hybridization (FISH). The aim of this correlation study was to test HER2 status in primary breast carcinomas with 2 BRISH methods, FISH, and 2 immunohistochemical assays using tissue microarray technology.
Materials and methods: Tissue cores (1.5 mm) were collected from 218 consecutive, archival formalin-fixed paraffin-embedded primary breast carcinomas into 4 duplicate tissue microarrays. Tumor tissue samples from 201 patients were successfully prepared in all 5 investigated methods comprising DuoCISH (Dako), Dual ISH (Ventana), HER-2 pharmDxFISH (Dako), HercepTest (Dako), and PATHWAY (4B5; Ventana).
Results: In this study the overall agreement between Dual ISH and FISH was 98.5% with a specificity of 99% and a sensitivity of 96%. DuoCISH had an equivalent high-positive agreement with FISH (sensitivity of 96%), but a lower specificity of 93% and an overall agreement of 93% with FISH. The overall agreement between the 2 immunohistochemical methods and FISH was almost perfect (Dako HercepTest 97% and Ventana PATHWAY (4B5) 98%). With regard to specificity the 2 methods performed equally (99.4%).
Conclusions: BRISH methods provide an alternative to FISH in evaluating HER2/CEN17 ratio in primary breast carcinomas. Dual ISH showed an almost perfect agreement with FISH and is a fast track method realistic to perform on all breast carcinomas. BRISH provide a permanent result that makes the method eligible for use in internal and external quality assurance.