Dual-colour chromogenic in-situ hybridization is a potential alternative to fluorescence in-situ hybridization in HER2 testing.

Aim: Dual-colour chromogenic in-situ hybridization (dc-CISH) is an emerging methodology for characterizing genomic alterations. This study was aimed at evaluating the performance of a dc-CISH kit (ZytoVision) in determining human epidermal growth factor receptor 2 (HER2) status in breast cancer. Methods and results: Two hundred and twenty-eight invasive breast carcinomas arranged in tissue microarrays were analysed in parallel with dc-CISH, fluorescence in-situ hybridization (FISH), and immunohistochemistry. Of 227 tumours with available FISH and dc-CISH results, HER2 amplification and nonamplification were detected in 49 (21.6%) and 178 (78.4%) tumours, respectively, by both assays. The concordance between dc-CISH and FISH results showed 100% agreement (j-coefficient = 1.00). Immunohistochemically, 162 (71%), 25 (11.0%) and 41 (18%) tumours were scored 0 / 1+, 2+, and 3+, respectively. The corresponding results with both FISH and dc-CISH demonstrated HER2 amplification in two (3.2%), nine (36%) and 38 (93%) tumours, respectively. Complete consensus among these three methods was observed in 197 cases, representing 98% of all 3+ and 0 / 1+ tumours (j-coefficient = 0.92). Confirmatory testing of 25 2+ tumours showed complete consensus between FISH and dc-CISH. Conclusions: dc-CISH is a promising alternative to FISH in HER2 testing, and the single-institute incidence of HER2 amplification in breast cancer in Taiwan is 21.2%.