PD‐L1 expression and FGFR‐mutations among Danish patients diagnosed with metastatic urothelial carcinoma: A retrospective and descriptive study

Checkpoint inhibitors have changed the treatment landscape of advanced urothelial carcinoma (mUC), and recently, a fibroblast‐growth‐factor‐receptor (FGFR) inhibitor has been introduced. This study aimed at estimating programmed death‐ligand 1 (PD‐L1) expression in primary tumors (PTs) and the PD‐L1 expression concordance between PTs and paired metastases in 100 patients with UC managed in the real‐world setting. Further, the aim was to investigate FGFR1–3 aberrations and the correlation between FGFR1–3 aberrations and PD‐L1 expression. PD‐L1 immunohistochemistry was performed on 100 formalin‐fixed paraffin‐embedded archival primary UC samples and 55 matched metastases using the 22C3 PD‐L1 assay. PD‐L1 expression was determined by the combined positive score, considered positive at ≥10. Targeted next‐generation sequencing on the S5+/Prime System with the Oncomine Comprehensive Assay version 3 was used to detect FGFR1‐3 aberrations in PTs. We found that 29 of 100 PTs had positive PD‐L1 expression. The PD‐L1 concordance rate was 71%. FGFR1‐3 aberrations were observed in 18% of PTs, most frequently FGFR3 amplifications or mutations. We found no association between FGFR1‐3 aberrations and PT PD‐L1 expression (p = 0.379). Our data emphasize the need for further studies in predictive biomarkers.