Multidimensional profiling of clinical trial cohorts and the characterization of radiotherapy/immunotherapy response biology in localised and metastatic muscle-invasive bladder cancer.

Abstract

824 Background: Whilst combined radiotherapy/immunotherapy shows promising clinical potential, biological determinants of response are poorly understood. In RADIO (chemoradiotherapy ± durvalumab in localised MIBC, ISRCTN43698103) and PLUMMB (hypofractionated radiotherapy + pembrolizumab in metastatic MIBC, NCT02560636) trials, baseline tumour and longitudinal blood was profiled to investigate response biology. Methods: Whole exome sequencing, bulk RNAseq, T-cell receptor (TCR)seq and multiplex immunofluorescence (mIF) were used to profile n=12 RADIO and n=21 PLUMMB tumours, and longitudinal blood. Outcomes included RECIST criteria, disease-specific survival at 21 weeks (PLUMMB) and recurrence data at 6 months (RADIO) follow up. Results: Tumour mutational burden (TMB)-high PLUMMB patients survived longer (p=0.027), and TMB correlated with APOBEC enrichment (p<0.0001). However, neoantigen burden and APOBEC score were not associated with survival or response, and did not correlate with each other in either trial. PLUMMB tumours were enriched for carbohydrate metabolism (FDR<0.01) and TGF-β signalling (FDR<0.00005) transcriptomic pathways compared to RADIO, where TGF-β signalling associated with unfavourable outcomes (FDR=0.0452). Radioresistance pathways including cell cycle, hypoxia and epithelial to mesenchymal transition characterised progressive disease in PLUMMB. Durable response in RADIO was characterised by more intratumoural B and T-cells (mIF, p=0.024, p=0.008), with more unique TCRs in the tumour (p=0.049) and baseline blood (p=0.04), which reduced upon response (p=0.0357). PLUMMB patients had more peripheral TCR clones (p=0.0006) and clonotypes (p=0.03) with lower tumour similarity than in RADIO. High peripheral baseline TCR count associated with PLUMMB PD (p=0.044), indicating extensive but ineffective immunity. Conclusions: This unique multidimensional dataset revealed established biology associated with response to single agent therapies, in addition to novel parameters characterising localised and metastatic MIBC response to radiotherapy/immunotherapy combinations. As bladder-sparing chemo/radio/immunotherapy options show promising potential, comprehensive profiling of bladder cancers with multiple orthogonal methods reveals complex multimodal response biology. Ultimately, multidimensional research is essential for developing combination therapy biomarkers, where those for single agents may not suffice.