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Background & Aims Surgical resection is the only potentially curative therapy for patients with biliary tract cancer (BTC), but 5-year survival rates after tumor resection have remained below 30%, corroborating the need for better stratification tools to identify the ideal surgical candidates. The soluble urokinase plasminogen activator receptor (suPAR) represents a mediator of inflammation and has been associated with distinct types of cancer. In this study, we evaluated a potential role of suPAR as a novel biomarker in patients undergoing BTC resection. Methods Tumor expression of uPAR was analyzed by immunohistochemistry in 108 BTC samples. Serum levels of suPAR were analyzed by ELISA in a training and validation cohort comprising a total of 117 patients with BTC and 76 healthy controls. Results High tumoral uPAR expression was associated with an adverse outcome after BTC resection. Accordingly, circulating levels of suPAR were significantly elevated in patients with BTC compared to healthy controls, as well as in patients with primary sclerosing cholangitis. Using a small training set, we established an optimal prognostic suPAR cut-off value of 3.72 ng/ml for patients with BTC. Importantly, preoperative suPAR serum levels above this cut-off value were associated with significantly impaired overall survival in both the training and validation cohort. Multivariate Cox-regression analysis including various clinicopathological parameters such as tumor stage, markers of inflammation and organ dysfunction, as well as tumor markers, revealed circulating suPAR levels as an independent prognostic marker following BTC resection. Finally, high preoperative suPAR levels were indicative of acute kidney injury after tumor resection. Conclusion Circulating suPAR represents a previously unrecognized biomarker in patients with resectable BTC, which might help to preoperatively identify the ideal candidates for liver surgery. Lay summary Surgical resection represents the only curative treatment option for patients with biliary tract cancer, but not all patients benefit to the same extent in terms of overall survival. Here, we provide evidence that serum levels of an inflammatory mediator (suPAR) are indicative of a patient's postoperative outcome and might thus help to identify the ideal surgical candidates., Graphical abstract, Highlights • Biliary tract cancer is associated with poor outcomes and increasing incidence. • Surgical resection is the only potentially curative treatment option for patients with biliary tract cancer. • The identification of ideal surgical candidates has remained challenging. • Circulating suPAR represents a novel diagnostic and prognostic biomarker in resectable patients. • SuPAR might be useful to identify patients with biliary tract cancer who will benefit most from tumor resection.

Summary Biliary tract cancers (BTCs) are aggressive epithelial malignancies that can arise at any point of the biliary tree. Albeit rare, their incidence and mortality rates have been rising steadily over the past 40 years, highlighting the need to improve current diagnostic and therapeutic strategies. BTCs show high inter- and intra-tumour heterogeneity both at the morphological and molecular level. Such complex heterogeneity poses a substantial obstacle to effective interventions. It is widely accepted that the observed heterogeneity may be the result of a complex interplay of different elements, including risk factors, distinct molecular alterations and multiple potential cells of origin. The use of genetic lineage tracing systems in experimental models has identified cholangiocytes, hepatocytes and/or progenitor-like cells as the cells of origin of BTCs. Genomic evidence in support of the distinct cell of origin hypotheses is growing. In this review, we focus on recent advances in the histopathological subtyping of BTCs, discuss current genomic evidence and outline lineage tracing studies that have contributed to the current knowledge surrounding the cell of origin of these tumours.