Risk stratification of pT1b urothelial carcinoma based on spatial relationships between invasive tumour and muscularis propria on TURB specimens for predicting muscle-invasive urothelial carcinoma in radical cystectomy: A new proposal

Introduction: In bladder cancer, the presence of lamina propria invasion (pT1) poses a significant clinical challenge due to varied tumour behaviours and risk of disease progression. Efforts to substage pT1 urothelial carcinoma (UC) using diverse systems have been made, but challenges persist in accurately predicting disease progression. This study introduces a novel risk stratification approach focusing on pT1b UC cases based on the spatial relationship between invasive carcinoma and the muscularis propria (MP) in transurethral resection of bladder (TURB) specimens. Materials and Methods: Retrospective analysis of pathology reports from 2017 to 2023 identified pT1 cases in TURB specimens, subcategorised using a 2-tiered approach. Exclusions were applied based on specific criteria, leading to a final cohort of 24 patients. We evaluated the tumour diameter and proximity to the MP from a “Tumour-MP (T-M) angle” perspective. A novel pT1b risk stratification method focusing on the T-M angle to differentiate low-and high-risk groups was developed, in which pT1b low-risk is defined as a T-M angle less than 180 degrees, and pT1b high-risk is defined as a T-M angle greater than 180 degrees. Results: In this study of 24 pT1b UC cases, 16 were categorised as pT1b low-risk and 8 as pT1b high-risk. Notably, the high-risk group showed a higher upstaging rate to advanced tumour stages (≥pT2) in radical cystectomy (RC) specimens compared to the low-risk group (88% vs. 56%, p = 0.015). Conclusion: This new risk stratification method presents promise in guiding early aggressive treatment decisions, though larger prospective studies are essential for further validation and clinical integration.