Histoanatomic and Quantitative Substaging of Lamina Propria Invasion in pT1 Bladder Urothelial Carcinoma: Associations with Recurrence and Progression

Objectives: This study aimed to evaluate lamina propria invasion in pT1 bladder urothelial carcinoma using different substaging methods and to compare the relationships of these methods with recurrence and progression. Methods: In 140 retrospectively evaluated cases of pT1 urothelial carcinoma, muscularis mucosae-based histoanatomic substaging, maximum invasion depth, maximum horizontal invasion width, number of invasive foci, and T1m/T1e-based micrometric classifications were examined. Results: Recurrence was detected in 55 patients (39.3%) and progression in 30 patients (21.4%). No significant difference was found among the histoanatomic substaging groups with respect to recurrence rates (p = 0.884), whereas the progression rate was markedly higher in the pT1c group compared with the pT1a and pT1b groups (52.2%; p < 0.001). In the logistic regression analysis adjusted for age and tumor number, pT1c was independently associated with progression compared with pT1a (OR 6.999; 95% CI 2.328–21.044; p = 0.001). Maximum invasion depth and maximum horizontal invasion width were also significantly higher in cases that developed progression and retained their independent associations with progression in the adjusted models. For each 1 mm increase, the OR was 1.209 (95% CI 1.063–1.375; p = 0.004) for maximum invasion depth and 1.084 (95% CI 1.007–1.167; p = 0.033) for maximum horizontal invasion width. An increasing trend in progression toward T1e was observed in the T1m/T1e classifications, but this did not reach significance in the adjusted models. Conclusions: Our findings support that both pT1c invasion extending beyond the muscularis mucosae and continuous quantitative invasion measurements can provide prognostic information in assessing progression risk in pT1 bladder urothelial carcinoma.