Improved method of detecting the ERG gene rearrangement in prostate cancer using combined dual-color chromogenic and silver in situ hybridization.

The recently detected TMPRSS2-ERG fusion gene was revealed as a recurrent and prevalent prostate cancer (PCa)-specific event, potentially qualifying it for clinical use. To detect this alteration, fluorescence in situ hybridization (FISH) is the method of choice. However, FISH has some disadvantages for widespread adoption in clinical practice. Subsequently, chromogenic in situ hybridization, which uses organic chromogens, and enzymatic metallography silver in situ hybridization have emerged as promising bright-field alternatives. Compared with chromogenic in situ hybridization, silver in situ hybridization signals are very distinct and superior with regard to signal clarity and resolution, but the method excludes multicolor protocols. Based on the ERG break-apart FISH assay, we established a dual-color ERG break-apart assay using combined chromogenic in situ hybridization and silver in situ hybridization (CS-ISH) and compared these results with those obtained by FISH. We assessed 178 PCa and 10 benign specimens for their ERG rearrangement status by applying dual-color FISH and CS-ISH ERG break-apart assays to consecutive sections. We observed a highly significant concordance (97.7%) between FISH- and CS-ISH-based results (Pearson's correlation coefficient = 0.955, P < 0.001). Our findings demonstrate that the ERG rearrangement status can reliably be assessed by CS-ISH. Further, the CS-ISH technique combines the accuracy and precision of FISH with the ease of bright-field microscopy. This tool allows a much broader spectrum of applications in which to study the biological role and clinical use of ERG rearrangements in PCa.