RT Journal Article T1 Frequency of microsatellite instability (MSI) in upper tract urothelial carcinoma: comparison of the Bethesda panel and the Idylla MSI assay in a consecutively collected, multi-institutional cohort A1 Kullmann, Friederike A1 Strissel, Pamela L. A1 Strick, Reiner A1 Stoehr, Robert A1 Eckstein, Markus A1 Bertz, Simone A1 Wullich, Bernd A1 Sikic, Danijel A1 Wach, Sven A1 Taubert, Helge A1 Olbert, Peter A1 Heers, Hendrik A1 Fernanda Lara, Maria A1 Luisa Macias, Maria A1 Matas-Rico, Elisa A1 Jose Lozano, Maria A1 Prieto, Daniel A1 Hierro, Isabel A1 van Doeveren, Thomas A1 Bieche, Ivan A1 Masliah-Planchon, Julien A1 Beaurepere, Romane A1 Boormans, Joost L. A1 Allory, Yves A1 Herrera-Imbroda, Bernardo A1 Hartmann, Arndt A1 Weyerer, Veronika K1 urological neoplasms K1 pathology K1 molecular K1 methods K1 Protein expression K1 Cancer K1 Tumors K1 Predictor K1 Survival K1 Prostate AB Aims Upper tract urothelial carcinoma (UTUC) is a rare malignancy with a poor prognosis which occurs sporadically or in few cases results from a genetic disorder called Lynch syndrome. Recently, examination of microsatellite instability (MSI) has gained importance as a biomarker: MSI tumours are associated with a better response to immunomodulative therapies. Limited data are known about the prevalence of MSI in UTUC. New detection methods using the fully automated Idylla MSI Assay facilitate analysis of increased patient numbers. Methods We investigated the frequency of MSI in a multi-institutional cohort of 243 consecutively collected UTUC samples using standard methodology (Bethesda panel), along with immunohistochemistry of mismatch repair (MMR) proteins. The same tumour cohort was retested using the Idylla MSI Assay by Biocartis. Results Using standard methodology, 230/243 tumours were detected as microsatellite stable (MSS), 4/243 tumours as MSI and 9/243 samples as invalid. In comparison, the Idylla MSI Assay identified four additional tumours as MSS, equalling 234/243 tumours; 4/243 were classified as MSI and only 5/243 cases as invalid. At the immunohistochemical level, MSI results were supported in all available cases with a loss in MMR proteins. The overall concordance between the standard and the Idylla MSI Assay was 98.35%. Time to result differed between 3 hours for Idylla MSI Assay and 2 days with the standard methodology. Conclusion Our data indicate a low incidence rate of MSI tumours in patients with UTUC. Furthermore, our findings highlight that Idylla MSI Assay can be applied as an alternative method of MSI analysis for UTUC. PB Bmj publishing group SN 0021-9746 YR 2021 FD 2021-09-28 LK https://hdl.handle.net/10668/27013 UL https://hdl.handle.net/10668/27013 LA en DS RISalud RD Apr 4, 2025