Predictive value of fibroblast growth factor receptor (FGFR) mutations and gene fusions on anti-PD-(L)1 treatment outcomes in patients (pts) with advanced urothelial cancer (UC).

419 Background: FGFR alterations have been shown to be associated with immunologically “cold” UC tumors with low immune marker expression and T cell infiltrate, a poorly receptive environment for immune checkpoint inhibitors. Using a real world matched clinical and genomic dataset of pts with advanced UC, we explored their predictive value in pts receiving anti-PD-(L)1 therapy. Methods: The Flatiron Health-Foundation Medicine Clinico-Genomic...