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The World Health Organization/International Society of Urological Pathology (2022 WHO/ISUP) classification categorizes noninvasive carcinomas based on the highest grade observed in a pathology sample. According to this classification, a lesion is classified as mixed-grade (MG) if the highest-grade component comprises less than 5% high-grade (HG) carcinoma [14]. This study included 160 cases of low-grade papillary urothelial carcinoma (LGUC) and 160 cases of HG papillary urothelial carcinoma (HGUC), selected randomly. In addition, 160 consecutive and unselected cases of MG papillary urothelial carcinoma (MGUC) were obtained from all bladder transurethral resection specimens diagnosed with papillary urothelial carcinoma between January 2007 and January 2021. The results of the multivariate analysis showed that histologic grade, invasion of the lamina propria, and the presence of carcinoma in situ at presentation were independent prognostic parameters regarding recurrence-free survival (p = 0.002; hazard ratio (HR) = 1.44, 95% confidence interval (CI) = 1.059-1.956, p = 0.02; and HR = 1.76, 95% CI = 1.159-2.684, p = 0.008, respectively). Histologic grade was the only independent prognostic parameter of disease-specific survival (DSS) (p < 0.001). Comparisons between non-muscle invasive (NMI) MGUC and NMI LGUC, as well as between NMI MGUC and NMI HGUC, revealed statistically significant differences in terms of DSS (HR = 0.07, 95% CI = 0.024-0.252, p < 0.001 and HR = 1.59, 95% CI = 1.023-2.460, p = 0.039, respectively). Our study findings demonstrate statistically significant differences regarding DSS between NMI MGUC and NMI HGUC, as well as between NMI MGUC and NMI LGUC. Therefore, we suggested that considering the presence of less than 5% MGUC as a separate category may be appropriate. However, it is important to validate our results in larger cohorts with longer follow-up periods to establish the clinical significance of MGUC and provide guidance for patient management., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)