Visualization of FISH Probes by Dual-Color Chromogenic In Situ Hybridization

The overall purpose of the study was to demonstrate applicability of the DAKO dual-color chromogenic in situ hybridization (CISH) assay (DAKO Denmark, Glostrup) with respect to 4 fluorescence in situ hybridization (FISH) probes: MYC (c-MYC), EGFR, ERBB2 (HER2), and TOP2A. The study showed that the dual-color CISH assay can convert Texas red and fluorescein isothiocyanate (FITC) signals into chromogenic signals with an almost complete 1:1 conversion ratio. Agreement studies between the FISH assays for HER2 and TOP2A and the corresponding CISH conversion assays showed 100% concordance (kappa values of 1.0) between the CISH and FISH methods for HER2 and TOP2A status. The correlations of the gene copy number to centromere-17 ratios were similarly high, with a correlation coefficient (r) for HER2 and TOP2A of more than 0.95. Owing to the relatively small number of specimens in this study, it is important that the data are confirmed in a larger study.