Harmonization trial of FGFR1-3 testing strategies in cholangiocarcinoma patients: an Italian multicenter experience

Aims: Molecular analysis of FGFR2 aberrant transcripts became crucial for clinical stratification of intrahepatic cholangiocarcinoma (iCCA) patients. Several strategies, including fluorescent in situ hybridization (FISH) and next generation sequencing (NGS), are commonly used to investigate FGFR aberrations. Here, we evaluated the technical performance of clinically implemented diagnostic strategies in 8 referral Italian institutions on artificial reference formalin-fixed paraffin-embedded (FFPE) samples. Methods: Each participating institution was requested to apply its own diagnostic testing strategy on 8 sections obtained from artificial reference specimens built to harbor FGFR3(17)-TACC3(11) rearrangement and unbalanced FGFR2. A second-round slide set hosting FGFR2(17)-BICC1(3) aberrant transcript was shared to detect clinically relevant FGFR2 fusion. Artificial reference sample was previously validated by the University of Naples Federico II before arranging the shipment. Technical procedures (e.g. extraction methods, testing platforms and assays) were recorded. Results: Overall, cell resuspension yielded higher amounts of DNA and RNA (SNU16 61.5 ng/µl, 38100.0 pg/µl; RT112 118.0/µl, 2140.0 pg/µl, respectively) in comparison with SNU16+ RT112 mixing cell block (0.7 ng/µl DNA and 412.0 pg/µl RNA). Moreover, FFPE samples showed a higher fragmentation index (DIN 1.2 and RIN not calculated) compared with cell line resuspension (DIN 2.2 and 9.5 for SNU16 and RT112; RIN 3.9 and 6.8 for SNU16 and RT112). All participating institutions identified FGFR2(17)-BICC1(3) and FGFR3(17)-TACC3(11) aberrant transcripts. Moreover, ID#2, ID#4, ID#7 institutions also detected FGFR2(3)-CD44(1) rearrangement on RNA, whereas institutions ID#1, ID#2, ID#3, ID#5, ID#6, ID#8 identified FGFR2 CNVs on DNA. Conclusions: NGS represents the most suitable approach in molecular profiling of FGFR aberrant transcripts. Rings trial based on artificial reference samples play a pivotal role in optimizing routine diagnostic procedures filling the gap in clinical stratification of iCCA patients.