Instant‐quality fluorescence in‐situ hybridization as a new tool for HER 2 testing in breast cancer: a comparative study

Aims HER 2 instant‐quality fluorescence in‐situ hybridization ( IQFISH ) is a new fluorescence in‐situ hybridization ( FISH ) assay developed with a non‐toxic buffer that reduces the hybridization time to 1–2 h, enabling a turnaround time of 3 h 30 min from dewax to counting. The aim of this study was to compare assessment of HER 2 status using IQFISH and assessment using standard FISH . Methods and results We selected 160 breast cancer samples according to their HER 2 status as determined by immunohistochemistry ( IHC ) in a retrospective multicentre cohort (40 cases in each scoring category, i.e. 0/1+/2+/3+). Each participating site ( n  = 5) constructed its tissue microarray ( TMA ) of 32 archival cases and sent it to the central site (site 1). HER 2 IHC , HER 2 FISH and HER 2 IQFISH were performed blindly at site 1. IQFISH provided excellent quality signals without any background staining, thus allowing excellent reading conditions even on TMA . Statistical analysis showed almost perfect agreement between IQFISH and FISH (99.3%, κ  = 0.98). The only discordant case was an equivocal one with an HER 2 / CEP 17 ratio near the ASCO / CAP cut‐off. Conclusions The highly concordant data support IQFISH as a useful alternative to FISH , allowing reliable assessment of HER 2 status. Use of this method could lead to reporting of HER status to the oncologist within a day.