FGFR testing from matched tissue and urine samples within the prospective real world clinico-pathological register trial BRIDGister.
Authors: Wirtz Ralph M. , Watts Richard , Kellner Ronny , Ortmann Reinhard , Horns Torsten , Enderle Daniel , Meyer Lisa , Noerholm Mikkel , Morken Mario , Veltrup Elke , Hake Roland , Eidt Sebastian , Roggisch Jenny , Koch Stefan , Ecke Thorsten 
Published: June 2021

e16532 Background: The objective of the present study was to assess FGFR mutattions and fusions from matched urine and tissue samples from patients suspicious of bladder cancer and undergoing first TURB at the pilot center of the multicentric BRIDGister RealWorld Experience trial Methods: For this pilot study paraffin fixed pretreatment tissue samples from the first TURB of 28 pts participating in the BRIDGister trial and matched urine samples were prospectively collected and analyzed. RNA from FFPE tissues were extracted by commercial kits and analyzed by Therascreen FGFR IVD kit (Qiagen GmbH, Hilden). In addition urine samples were shipped for central isolation of extracellular vesicles and extraction of RNA (exoRNA.Exosome Diagnostics GmbH, Martinsried) and subsequently centrally analyzed by QIAcuity digital PCR (Qiagen, Hilden). Additional urine testing was performed by further technologies including central cytology. Concordance, Kruskal-Wallis, MannWhitney and Sensitivity/Specificity tests were analyzed by JMP 9.0.0 (SAS software). Results: The pilot cohort of the BRIDGister trial consisted of 28 patients (median age: 73, male 71% vs female 29%) of diverse clinical stages (Benign lesions/no tumor 21%, pTa 32%, pT1 21%, pT2 21%) and WHO 1973 grade (G1 7%, G2 43%, G3 21%). Based on FFPE tissue testing using Therascreen FGFR IVD kit 9 out of 28 patients exhibited FGFR alterations (32%). Based on exosomal RNA (exoRNA) and subsequent dPCR testing 8 out of 21 matched urine sampels were FGFR positive (38%). Comparison with tissue testing as probable gold standard revealed 71% sensitivity, 78% specificity, 63% PPV and 85%NPV. There were 3 patients being FGFR positive for exoRNA from urine with no mutation found in the corresponding TUR biopsy. One of these mutations could be validated by independent urine test. Furthermore one tumor harbored two tissue mutations (R248C, Y373C) but three urine mutations (R248C, Y373C, G370C) indicating substantial tumor heterogeneity. One FGFR3-TACC3 fusion was detected from a benign lesion, which was not found by the exosomal urine test. Conclusions: Extraction of exosomal RNA from urine followed by highly sensitive dPCR mutation testing is feasible with good concordance to matched tissue testing. Urine testing bears the potential of detecting additional mutations in a real world setting and might evolve as alternative approach for FGFR3 screening in a non invasive fashion without the need of transurethral biopsy. Discordant cases are further followed up and might reveal validation of mutation status in upcoming recurrences.Further exploration is warranted and includes the potential of monitoring patients with FGFR before and after therapeutic intervention. By the time of the congress an update of the data with approximately 50 matched pairs will be presented.