Prognostic value and therapeutic implications of an integrative molecular subtype and immune content classifier in localized muscle-invasive bladder cancer

530 Background: Localized muscle-invasive bladder cancer (MIBC) exhibits heterogeneous molecular features and outcomes, with a 5-year mortality rate of approximately 30%. Immune checkpoint blockade (ICB) has the potential to improve oncological outcomes but molecular tools are needed to identify those most likely to benefit. Here, we integrate transcriptomically derived tumor immune microenvironment (TIME) data with molecular subtypes to create a novel integrative classifier with prognostic and therapeutic implications. Methods: RNAseq data from patients with localized muscle-invasive bladder cancer (MIBC) from the Cancer Genome Atlas BLCA (TCGA-BLCA) project was utilized (n = 187). CIBERSORT was used for immune cell deconvolution, and unsupervised hierarchical clustering divided the cohort based on similar immune profiles. Consensus molecular clustering information for the cohort was obtained from Kamoun et al. Overall survival (OS) of each cluster were analyzed. The tumor immune dysfunction and exclusion (TIDE) tool, which uses a genomic signature validated on immunotherapy treated melanoma patients to model tumor immune evasion, was then used to predict response to ICB. Results: In the TCGA-BLCA cohort, there were two distinct clusters enriched with macrophages, CL1-M0Hi (n = 18) and CL5-M2Hi (n = 35). Compared to the rest of the cohort, these two macrophage enriched clusters combined exhibited a decreased OS (33.1 mo vs. NR, p = 0.01). TIDE tool predicted ICB response was lowest in CL1 (6/18, 33%; p = 0.09), CL5 (12/35, 34%; p = 0.02), and the Ba/Sq molecular cluster (16/57, 28%; p = 1.3x10-5). Patients designated as CL1 or CL5 by immune clustering and Ba/Sq by molecular consensus were combined into a subgroup (n = 20). Compared to the rest of the cohort, this Ba/Sq_MacrophageHi subgroup had a higher body mass index (31.0 vs. 25.8 BMI, p = 0.0004), more whites (95% vs. 64%, p = 0.03), and had a higher stage (80% Stage III/IV vs. 20% Stage I/II, p = 0.05). The Ba/Sq_MacrophageHi cluster demonstrated higher PD-L1 expression (mean Z score 0.15 vs. -0.09; p = 0.008), there was a higher degree of T cell exclusion (mean Z score 0.16 vs. -0.06; p = 0.003) and cancer-associated fibroblasts (mean Z score 0.03 vs. -0.02; p = 3.4x10-5). Overall, the predicted response to ICB by TIDE in the Ba/Sq_MacrophageHi was lower (OR 0.15, 0.03-0.55 p = 0.002) and OS was significantly shorter (median 16.7 mos vs. 54.9 mo, p = 0.04). Conclusions: We demonstrated the prognostic significance of the Basal/Squamous subtype with macrophage enrichment in patients with localized MIBC. Pending further prospective validation, this sub-population may be less amenable to ICB treatment.