1771P Genomic characteristics and clinical outcomes of HRAS-mutated urothelial bladder cancer

Abstract

HRAS gene encodes the GTPase HRAS protein, a member of the RAS superfamily, which is enriched in high-grade urothelial bladder carcinoma (UBC). We aimed to characterize genomic and clinical outcomes of patients with HRAS mutations (HRASmt) as a possible prognostic and therapeutic biomarker. A total of 3,426 UBC tissue samples underwent molecular profiling at Caris Life Sciences utilizing NGS of DNA. MAP kinase pathway activation and the likelihood of a tumor’s response to anti-PD(L)1 therapy were measured via MPAS and IFN signature, respectively. Wilcoxon, Fisher’s exact were used for statistical significance. Overall survival (OS) was calculated from the date of tissue collection or the start of treatment until the last contact from insurance claims. All comparisons were conducted between HRAS mutated tumors and the entire UBC general cohort (GC). HRASmt were detected in 107 patients with metastatic UBC (3.12%). Of those, 70% were detected in primary and 30% from metastatic sites. HRASmt were associated with lower TMB (5 vs 8 mut/Mb, q<0.01) and higher PD-L1 expression (55.3% vs 39.1%, q<0.01). HRASmt tumors harbored less TP53 (25.5% vs 60.1%, q<0.05), RB1 (5.3% vs 22.1%, q<0.05), FGFR3 (1.9% vs 13.9%, q<0.05), and KMT2D (14.0% vs 25.4%, q<0.05), but more BRAF mutations (14.0% vs 2.1%, q<0.05). The most frequent HRAS point mutation involved Q61 (47.6%). HRAS-Q61 mutant tumors showed higher MPAS scores (2.21 vs 0.6, q<0.001), enrichment in pathways (all q<0.05) such as EMT (0.86 vs 0.83), TGFb (0.91 vs 0.89), angiogenesis (0.78 vs 0.75) and notch signaling (0.82 vs 0.81). Patients with HRAS-Q61 point mutations experienced worse OS and prognosis compared to HRASwt tumors when treated with checkpoint inhibitors (HR 1.45, 95% 1.01-2.10; p <0.05). HRAS-Q61 point mutations represent a clinically relevant mutation in UBC, as evidenced by its association with worse clinical outcomes compared to HRASwt tumors. Our transcriptomic analysis suggests HRAS-Q61 mutations were associated with lower response to immunotherapy and leads to MAPK activation, as well as modulation of important TME pathways, possibly indicating a distinct biological and clinical phenotype. Our study provides rationale for therapeutic HRAS targeting in UBC.