**5. Conclusions**

Preoperative factors that relate to complex TURBT were identified by expert judgement and organized into the Bladder Complexity Checklist to facilitate the evaluation of the risk of a complex TURBT, a crucial requisite to personalise patient's information, adapt human and technical resources to individual situations and address TURBT variability in clinical trials.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2072-6694/12/10/3063/s1, Figure S1: First-round distribution of the experts' scores regarding the influence of the characteristics of the patient on the likelihood of complex TURBT; Figure S2: First-round distribution of the experts' scores regarding the influence of the characteristics of the tumour on the likelihood of complex TURBT; Figure S3: First-round distribution of the experts' scores regarding the influence on the likelihood of complex TURBT of bladder characteristics and access; Figure S4: First-round distribution of the experts' scores regarding the influence of the surgical environment on the risk of TURBT or En-Bloc resection resulting in either three situations: incomplete resection according to the operator, prolonged surgery (>1 h) or significant intra- (bleeding that requires transfusion, laparotomy) or postoperative complications (Clavien-Dindo Grade III and higher); Table S1: Articles (English language, 4/2009-4/2019) found relevant to the definition of complexity in transurethral resection of bladder tumours; Table S2: 150 scenarios constructed for univariate and multivariate analyses of clinical features in relation to complexity.

**Author Contributions:** Conceptualization: E.X., M.C., M.B. (Marek Babjuk), J.P.R., F.W., B.M.; methodology M.R., B.M.; investigations: M.R., E.X., A.B., M.B. (Maximillian Burger), H.M., M.C., M.B. (Marek Babjuk), J.P.R., F.W., B.M.; writing—original draft preparation: M.R., B.M.; writing—review and editing: B.M.; supervision: B.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors express their gratitude to Doctor Thomas Filleron for critical discussion on the methodology and to Professor Laurent Boccon-Gibod for his comments and review of the manuscript.

**Conflicts of Interest:** The Authors declare no conflict of interest.
