AIMS: To compare the 1973 WHO and the 2004/2016 WHO grading systems in patients with urothelial carcinoma of urinary bladder (UCUB), since no consensus has been made which classification should supersede the other and since both are recommended in clinical practice. METHODS: Newly diagnosed patients with Ta UCUB treated with transurethral resection of bladder tumour were abstracted from the Surveillance, Epidemiology and End Results database (2010-2016). Kaplan-Meier plots and multivariable Cox regression models (CRMs) tested cancer-specific mortality (CSM), according to 1973 WHO (G1 vs G2 vs G3) and to 2004/2016 WHO (low-grade vs high-grade) grading systems. RESULTS: Of 35 986 patients, according to 1973 WHO grading system, 8165 (22.7%) were G1, 17 136 (47.6%) were G2 and 10 685 (29.7%) were G3. According to 2004/2016 WHO grading system, 24 961 (69.4%) were low-grade versus 11 025 (30.6%) high-grade. In multivariable CRMs, G3 (HR: 2.05, p<0.001), relative to G1, and high-grade(HR: 2.13, p<0.001), relative to low-grade, predicted higher CSM. Conversely, G2 (p=0.8) was not an independent predictor. The multivariable models without consideration of either grading system were 74% accurate in predicting 5-year CSM. After addition of 1973 WHO or 2004/2016 WHO grade, the accuracy increased to 76% and 77%, respectively. CONCLUSIONS: From a statistical standpoint, it appears that the 2004/2016 WHO grading system holds a small, although measurable advantage over the 1973 WHO grading system. Other considerations, such as intraobserver and interobserver variability may represent an additional matric to consider in deciding which grading system is better.

Cancer Prognostics and Health Outcomes Unit Division of Urology University of Montréal Health Center CRCHUM Montreal Quebec Canada

Department of Medicine and Surgery Scuola Medica Salernitana University of Salerno Fisciano Campania Italy

Department of Urology 2nd Faculty of Medicine Charles University Prag Czech Republic

Department of Urology and Division of Experimental Oncology URI Urological Research Institute IBCAS San Raffaele Scientific Institute Milan Lombardia Italy

Department of Urology Comprehensive Cancer Center Medical University of Vienna Vienna Austria

Department of Urology University Hospital Frankfurt Goethe University Frankfurt Faculty 16 Medicine Frankfurt am Main Hessen Germany

Department of Urology University of Texas Southwestern Dallas Texas USA

Departments of Urology Weill Cornell Medical College New York New York USA

Division of Urology Department of Special Surgery Jordan University Hospital The University of Jordan Amman Jordan

Institute for Urology and Reproductive Health 1 M Sechenov 1st Moscow State Medical University Moscow Russia

Martini Klinik Prostate Cancer Center University of Hamburg Faculty of Medicine Hamburg Germany

Urology Unit Department of Neurosciences Reproductive Sciences and Odontostomatology University of Naples Federico 2 Naples Campania Italy

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Comparison between 1973 and 2004/2016 World Health Organization grading in upper tract urothelial carcinoma treated with radical nephroureterectomy