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).

419Background: 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 Database (CGDB) contained full clinical and treatment information and molecular data on a cohort of pts with confirmed advanced UC. The populations of interest are FGFR+ and FGFR- patients determined by the presence or absence of a prespecified panel of FGFR2/3 mutations and fusions. Overall survival (OS), measured from the start of anti-PD-(L)1 therapy, was analyzed using Kaplan-Meier estimation and Cox proportional hazards models adjusted for left truncation (delayed entry model). Results: 118 pts (FGFR+ n = 26, FGFR- n = 92) treated with anti-PD-(L)1 therapy for adv...