RNA-seq profiling of upper tract urothelial carcinoma: bladder cancer consensus classification relevance, molecular heterogeneity and differential immune signatures.

Analyses of large transcriptomics datasets of muscle-invasive bladder cancer (MIBC) has led to a consensus classification. Molecular subtypes of upper tract urothelial carcinomas (UTUC) are less known. Our objective was to determine the relevance of consensus classification in UTUCs by characterizing a novel cohort of surgically treated ≥pT1 tumors. Subtype IHC markers GATA3-CK5/6-TUBB2B in multiplex, CK20, p16 and Ki67, MMR proteins, PD-L1 IHC were evaluated. Heterogeneity was assessed morphologically and/or with subtype IHC. FGFR3 mutations were identified by pyrosequencing. We performed 3'RNA-seq, including with multisampling in heterogeneous cases. Consensus classes, unsupervised groups, and microenvironment cell abundance were determined using gene expression. Most of the 66 patients were men (77.3%), with pT1 (n=23, 34.8%) or pT2-4 stage UTUC (n=43, 65.2%). FGFR3 mutations and dMMR status were identified in 40% and 4.7% of cases, respectively. Consensus subtypes robustly classified UTUCs and reflected intrinsic subgroups. All pT1 tumors were classified as Luminal papillary (LumP). Combining our consensus classification results to that of previously published UTUC cohorts, LumP tumors represented 57.2% of ≥pT2 UTUC, which was significantly higher than in MIBC. Ten patients (15.2%) harbored areas of distinct subtypes. Consensus classes were associated with FGFR3 mutations, stage, morphology and IHC. The majority of LumP tumors were characterized by low immune infiltration and PD-L1 expression, in particular if FGFR3 mutated. Our study shows that MIBC consensus classification robustly classified UTUCs, and highlighted intratumoral molecular heterogeneity. Proportion of LumP was significantly higher than in MIBCs. Most LumP tumors showed low immune infiltration and PD-L1 expression and high proportion of FGFR3 mutations. These findings suggest differential response to novel therapies between UTUC and MIBC patients.