Targeted treatment of advanced or metastatic urothelial carcinomas (UCs) requires the identification of druggable mutations. This study describes the development of a 3′ Rapid Amplification of cDNA Ends (3′ RACE)-based targeted RNA sequencing panel which accounts for the status of all genes relevant to UC treatment, namely, FGFR1-4, KRAS, NRAS, BRAF, ERBB2 (HER2), CD274 (PD-L1) and PIK3CA. FGFR2/3-activating point mutations or fusions were found in 54/233 (23.2%) tumors. FGFR3 rearrangements were identified in 11 patients, with eight of them being undetectable by commonly used PCR kits. In addition, one tumor contained a high-copy FGFR2 gene amplification accompanied by strong overexpression of the gene. Mutations in RAS/RAF genes were present in 30/233 (12.9%) UCs and were mutually exclusive with alterations affecting FGFR2/3 genes. On the contrary, activating events in the HER2 oncogene (point mutations and overexpression), as well as PIK3CA mutations, which were relatively common, occurred with similar frequencies in RAS/RAF- or FGFR2/3-positive vs. negative samples. High PD-L1 mRNA expression was associated with advanced disease stage and was not observed in tumors with increased HER2 mRNA expression or in UCs with evidence for FGFR2/3 activation. Three of the studied carcinomas had high-level microsatellite instability (MSI). Overall, more than half of the UCs had potentially druggable genetic alterations. The proposed NGS panel permits comprehensive and cost-efficient analysis of UC-specific molecular targets and may be considered in clinical routine.
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