Vertical Lamina Propria Invasion Diagnosed by En Bloc Transurethral Resection is a Significant Predictor of Progression for pT1 Bladder Cancer.

Purpose: T1 bladder cancer is characterized by high recurrence and aggressive progression. Muscularis mucosae invasion may be a prognostic factor for progression, but the limitations of conventional transurethral resection of bladder tumors make diagnosis difficult. We correlated degree of invasion with oncologic outcome and evaluated the utility of pathological diagnosis following en bloc resection of bladder tumors.
Materials and Methods: We retrospectively analyzed the records of 123 consecutive patients diagnosed with pT1 bladder cancer between November 2013 and December 2018. Transurethral resection was conducted in 91 patients, and en bloc resection in 32 patients. All specimens were analyzed for invasion depth and pT1 substaging (T1a/b: invasion above or into/beyond muscularis mucosae, pT1m/e: microinvasive or extensively invasive). Primary end points were prognostic values of pT1 substaging and invasion depth. The secondary end point was the pathological diagnostic utility of en bloc resection.
Results: Median followup was 23 months. Three-year progression-free survival rate differed significantly depending on muscularis mucosae invasion (pT1a: 97.3%, pT1b: 72.8%; p=0.003) and invasion depth from basal membrane (<2 mm: 90.6%, ≥2 mm: 77.9%; p=0.03). Multivariate analysis showed that sessile tumor and invasion depth from basal membrane ≥2 mm were independent prognostic factors for progression. Diagnostic rates for pT1a/b and invasion depth were 77.6% and 85.9%, respectively, with transurethral resection, but 100% and 100% with en bloc resection (p=0.01 and p=0.03).
Conclusions: Vertical lamina propria invasion is predictive of progression in T1 bladder cancer, underlining the importance of accurately diagnosing the degree of vertical lamina propria invasion with en bloc resection.