Under-reporting of Carcinoma in Situ in Patients with High-Grade Papillary Non-Muscle-invasive Bladder Cancer.

Background Concomitant carcinoma in situ (CIS) with high-grade papillary urothelial carcinoma impacts patient risk stratification and treatment. However, on identification of a high-grade papillary lesion, pathologists may be disinclined to search for possible CIS. Several newer agents for bacillus Calmette-Guérin–unresponsive non–muscle-invasive bladder cancer (NMIBC) are indicated specifically for patients with CIS ± papillary tumors; hence failure to detect/report CIS may limit treatment options. Objective To assess CIS frequency in patients with high-grade Ta/T1 NMIBC. Methods In this retrospective cohort study, transurethral resection of bladder tumor biopsy specimens with an accompanying diagnosis of high-grade papillary NMIBC without CIS were identified in the PathNet database (2023–2024) and re-reviewed by a single pathologist for the presence of concomitant CIS. Results In total, 316 cases of high-grade papillary urothelial carcinoma (254 Ta, 62 T1 disease) were identified for re-review. Mean patient age was 73 (range 27–93) years; 81.0% of patients were male. On re-review, CIS was identified in 80 cases (25.3%, 95% CI 20.8%–30.4%). CIS frequency was higher in T1 disease (19/62 cases [30.6%]) vs Ta disease (61/254 cases [24.0%]). Among the 8 pathologists who performed the initial review, CIS-positivity rates in their individual biopsy samples varied from 15.0% (6/40) to 66.7% (2/3). Conclusion This study suggests that ∼25% of patients with high-grade papillary urothelial carcinoma may have unreported CIS. Close communication between the urologist and pathologist is crucial in ensuring specific exclusion of CIS in all bladder specimens, since a diagnosis of concomitant CIS may impact patient management.