Muscle-invasive bladder cancer (MIBC) is characterised by significant molecular heterogeneity, with the tumour composition being further scu
Muscle-invasive bladder cancer (MIBC) is characterised by significant molecular heterogeneity, with the tumour composition being further sculptured by local microenvironmental influences. This inherent complexity contributes to the divergent disease trajectories and the variable therapeutic susceptibility observed among patients. Consequently, there is an evident need for prognostic and predictive biomarkers to guide clinical strategies based on the tumour’s molecular fingerprint. Standard treatment for MIBC consists of cisplatin-based neoadjuvant chemotherapy (NAC) followed by radical cystectomy. This thesis aimed to further explore tumour cell-intrinsic features and the local immune landscape to gain a deeper understanding of potential determinants of prognosis and NAC response. Tissue-based proteomic and genomic analyses on all (n=145) or selected (n=15) tumour specimens from a retrospective cohort of patients who underwent radical cystectomy with (n=65) or without (n=80) NAC were combined with in vitro experiments. In Paper I, examination of the local immune repertoire revealed that an immune-enriched microenvironment at the time of cystectomy, characterised by elevated densities of T and B lymphocyte populations and high expression levels of the checkpoint molecules PD-1 and PD-L1, was independently associated with a reduced risk of recurrence. However, the immune contexture did not predict NAC response. Paper II investigated the clinical implications of the putative proto-oncogene RNA-binding motif protein 3 (RBM3). Elevated tumour-specific RBM3 expression was significantly associated with an improved clinical outcome in patients treated with NAC compared to untreated cases. The implicated link between RBM3 and chemosensitivity was corroborated by in vitro studies, which demonstrated decreased chemosensitivity of T24 cells following RBM3 silencing. Transcriptomic analyses provided a potential mechanistic explanation, suggesting involvement of RBM3 in cell cycle progression. Paper III sought to elucidate the impact of spatial intratumour heterogeneity (ITH) on therapeutic benefit. In-depth genomic, phenotypic, and immune profiling was performed across geographically separated tumour regions in fifteen patients exhibiting divergent biological responses to NAC. Distinct patterns of ITH were identified, some of which correlated with NAC response. Opposing trends were observed between small-scale and chromosomal-level alterations, but with a significant proportion of optimal responses linked to DDR deficiency. Molecular subtype ITH was denoted among complete responders. Consistent with the findings of Paper I, the immune milieu provided limited predictive information. In conclusion, this thesis contributes to the ongoing characterisation of the biological sum of tumour cell-intrinsic and extrinsic features, the clinical significance of which must be carefully delineated. This will become increasingly important with the advent of novel neoadjuvant treatment strategies.
