Analysis of the Application of the Micrometric Substaging System to Predict Recurrence and Progression in a Cohort of Patients with pT1 High-Grade Non-Muscle Invasive Bladder Cancer

Background: The World Health Organization (WHO) classification system for bladder cancer (BC) advocates for the substaging of pT1 disease, which may improve the prediction of cancer recurrence and progression. This study aims to evaluate the application and prognostic significance of a micrometric substaging system, utilising a 1 mm cut-off depth of invasion in patients with pT1 BC.

Methods: We retrospectively reviewed all patients diagnosed with pT1 High-Grade Non-Muscle Invasive Bladder Cancer (NMIBC) at our institution. Lamina propria infiltration was categorised using a 1 mm cut-off to differentiate between Focal (<1 mm) or Extended (≥1 mm) disease, dividing the patients into Focal and Extended groups.

Results: The study included 114 patients, with a median (Interquartile Range (IQR)) age of 78 (71-87) and a Charlson Comorbidity Index (CCI) of 6 (5-7). The median follow-up was 33 (20-53) months. Of these, 56 patients (49.0%) were classified as having focal invasive, while 58 (51.0%) had Extended invasion. Demographic and pathological characteristics were evenly distributed between the two groups without significant differences (p > 0.05). However, Extended disease was more prevalent at initial diagnosis (Odds Ratio (OR) 5.44, p = 0.003). Multivariate analysis identified a first diagnosis of BC, pathological Grade 3 (G3), presence of Carcinoma in situ (CIS) and residual tumour at second resection as independent predictors of Extended pT1. Recurrence rates, progression rates and cancer-specific mortality were 41.2%, 5.3% and 1.8%, respectively. There were no statistically significant differences between the Focal and Extended groups in 3-year recurrence-free (58.9% vs 63.8%, p = 0.654), progression-free (92.9% vs 96.5%, p = 0.270) and cancer-specific survival (100% vs 98.3%, p = 0.425) rates.

Conclusions: In this retrospective, single-centre study, substaging by depth of invasion did not predict recurrence, progression or cancer-specific mortality in patients with pT1 NMIBC. The initial diagnosis of pT1 BC, presence of G3, CIS and residual tumour at the second resection were identified as independent predictors of Extended pT1.