Proteomic Profiling of Tissue Exosomes Indicates Continuous Release of Malignant Exosomes in Urinary Bladder Cancer Patients, Even with Pathologically Undetectable Tumour

SIMPLE SUMMARY: Urinary bladder cancer (UBC) has a high recurrence rate, and biomarkers for different treatment strategies are highly needed. This study investigated the release of nanovesicles called exosomes from urinary bladder tissue from tumour-proximal sites as well as tumour-distant sites in transurethrally resected (TUR-B) patients with or without preoperative neoadjuvant chemotherapy prior to ensuing radical cystectomy—all without remaining visible tumour after TUR-B. We show that cancer-promoting exosomes were detected from both sites, suggesting that the previous tumour has altered the whole bladder tissue into a cancer-supporting milieu. The exosomes may originate from remaining pathologically undetectable cancer cells or transformed epithelial cells, and the study supports the notion of exosomes as mediators of metastatic spread and as potential biomarkers. It also supports early and radical removal of the bladder in urinary bladder cancer patients. ABSTRACT: Invasive urothelial bladder cancer (UBC) has high recurrence rates even after radical cystectomy (RC). Exosomes are membrane-bound nanovesicles, which have been shown to contribute to carcinogenesis and metastasis. We previously showed that urinary exosomes display a malignant profile in UBC patients despite the absence of detectable tumour. Here, we investigated exosomes from sampling sites close to or distant from the former tumour, aiming to understand the effect of the tumour on the local milieu. Ten patients scheduled for cystectomy after transurethral bladder resection (TUR-B), without remaining detectable tumour, were included. Exosomes were isolated from tissue explants of both the previous tumour site and distant bladder tissue. Proteins were quantified by mass spectrometry in seven patients. Exosomes from the previous tumour site were enriched in inflammatory but not cancer-related pathways compared to distant tissue. However, the 69 most abundant proteins in tissue-derived exosomes regardless of site, 20 of which were also found in urinary exosomes from our previous study, were enriched for cancer-related metabolic pathways and associated with poor prognosis in an external mRNA dataset. The enrichment of cancer-related pathways in the most abundant proteins, regardless of sampling site, confirms our hypothesis that despite the absence of detectable tumour, the entire bladder releases exosomes that contribute to metastasis and highlights the need for early RC.