Mapping the evidence base of kidney, prostate and urinary tract tumours to inform the WHO classification of tumours

Background
The project ‘World Health Organization (WHO) Classification of Tumours (WCT): a Living Evidence Gap Map by Tumour Type’ applies the Evidence and Gap Map (EGM) methodology to systematically synthesise evidence to support iterative refinements of the WCT. As part of this work, we created the first EGM for the WCT of Urinary and Male Genital Tumors, covering clear cell renal cell carcinoma, non-clear cell renal cell carcinoma, glandular neoplasms of the prostate and urothelial tumours.

Methods
Systematic searches in PubMed and Ovid Embase were conducted and harmonised to a 2020 to 2024 publication time period. Following title and abstract screening, reviewers coded and extracted data from the included records for tumour type, characteristic and study design using EPPI-Reviewer®. Levels of evidence were assigned applying the adapted Hierarchy of Research Evidence for Tumour Pathology and visualised with EPPI-Mapper®.

Results
Of 65,686 deduplicated records, 4,138 studies met inclusion criteria, generating 6,117 EGM entries across 30 tumour types. Evidence on histopathology (28.9%) and prognosis (28.2%) dominated the entries, while prediction was underrepresented (1.6%) or absent in several tumour types. High-level evidence accounted for 17.3% of entries overall, while low-level evidence prevailed across all groups (40.9% in urothelial tumours to 68.0% in non-clear cell renal cell carcinomas). Overall, of 180 tumour-type-by-characteristic EGM cells, 24.4% showed absolute gaps, 42.8% relative gaps, 2.8% synthesis gaps and 30.0% solid evidence.

Conclusions
The available evidence for urinary tract and male genital tumours is heterogeneous, with robust research in clear cell renal cell carcinoma contrasting with sparse predictive evidence and absolute gaps for rare and recently introduced tumour types. This map highlights targeted systematic reviews, cancer registry-based case accumulation and standardised use of WCT nomenclature as priorities for strengthening urological tumour classification.