Interobserver variability in the recognition of urothelial carcinoma subtypes: a survey

Urothelial carcinoma (UC) of the urinary bladder comprises a heterogeneous group of histologic subtypes with distinct prognostic and therapeutic implications. Current World Health Organization (WHO) and International Society of Urological Pathology (ISUP) recommendations emphasize the recognition and reporting of UC subtypes, even when present as minor components. However, the practical application of these recommendations in routine diagnostic practice remains challenging, and interobserver variability persists. We conducted a cross-sectional, web-based survey to evaluate pathologists' awareness, diagnostic interpretation, and reporting practices regarding UC subtypes. The survey included 46 items encompassing demographics, conceptual knowledge, attitudes toward subtype reporting, and 39 image-based diagnostic questions covering a broad spectrum of UC subtypes. Reference standard diagnoses were established by consensus among genitourinary pathology experts. Agreement rates and patterns of diagnostic disagreement were analyzed descriptively. A total of 133 pathologists submitted responses, and 79 completed all survey items. The overall mean agreement rate with the reference standard across image-based questions was 65%. The highest levels of agreement with the reference standard were observed for micropapillary UC, lymphoepithelioma-like UC, and clear-cell (glycogen-rich) UC, whereas the lowest accuracy rates were seen for UC with trophoblastic differentiation, nested UC, and UC with glandular differentiation. A high level of diagnostic disagreement was noted among morphologically overlapping subtypes, particularly glandular, squamous, and large nested patterns. Despite these challenges, 94% of respondents reported that UC subtypes should be routinely documented, although substantial variability existed regarding threshold criteria for reporting. This survey demonstrates significant interobserver variability in the recognition and interpretation of urothelial carcinoma subtypes, especially for rare or morphologically overlapping variants. While certain subtypes show high diagnostic concordance, many remain within diagnostic gray zones that may affect reporting consistency and clinicopathologic communication. These findings underscore the need for continued education, refinement of consensus criteria, and practical guidance to improve diagnostic reproducibility and standardization in the reporting of UC subtypes.