Evaluation of Reliability of FISH Versus Brightfield Dual-probe In Situ Hybridization (BDISH) for Frontline Assessment of HER2 Status in Breast Cancer Samples in a Community Setting

Aims: To evaluate the reliability of novel brightfield microscopy–based dual in situ hybridization (BDISH) methods for frontline HER2 status analysis in selected suboptimally preserved breast cancer tissue samples reflecting of the worst scenario in a community. Methods and Results: A total of 320 morphologically poorly preserved breast invasive ductal carcinomas from the archives of 2 tertiary institutions in Brazil were selected for a tissue microarray–based analysis. 4B5 antibody was used for immunohistochemistry. Fluorescence in situ hybridization (FISH), DuoCISH, ZytoDot CISH, and silver in situ hybridization (SISH) were performed and compared. The highest agreement was observed between SISH and FISH. In addition, SISH was easier to assess in both amplified and nonamplified cases when compared with the other chromogenic methods, due to the sharpness of its dots. DuoCISH produced false-positive results, associated with thicker ill-defined dots, causing poor distinction between nonamplification and low amplification. ZytoDot CISH showed lower sensitivity, with increased frequency of false-positive results. Conclusions: SISH is the most reliable of the BDISH methods, with sensitivity and specificity highly comparable with FISH. It is also less deleterious than other BDISH methods, producing signals that were more distinct and therefore more readily analyzable even in poorly preserved tissue.