Oncological outcomes and prognostic implications of T1 histo-anatomic substaging in the management of high-Grade non-muscle invasive bladder cancer: results from a large single centre series.

PURPOSE

This study aimed to comprehensively evaluate the prognostic value of T1 histo-anatomic substaging (T1a/T1b) for high grade (HG) non-muscle invasive bladder cancer (NMIBC) over a large single-centre cohort.

MATERIALS AND METHODS

Patients with primary HG T1 NMIBC were identified from our Institutional database, between 2011 and 2022. Data from diagnosis to repeated transurethral resection of bladder tumour (RE-TURBT), bacillus Calmette-Guérin (BCG) treatment and follow-up were collected. Patients were stratified based on histo-anatomic landmark into T1a (invasion above the Muscularis Mucosa-MM) and T1b (into/beyond MM). Kaplan-Meier curves and multivariate Cox regression analyses were used to assess the impact of histo-anatomic substaging on recurrence-free survival (RFS), cancer-specific survival (CSS), and progression-free survival (PFS).

RESULTS

Substaging was feasible in 88% of cases. The median (IQR) follow-up was 40 (17-72) months. T1b patients had larger initial tumours (> 3 cm: 43.2% vs. 26.1%, p < 0.001), while upstaging to muscle-invasive bladder cancer (MIBC) at RE-TURBT was more frequent in T1b than in T1a (5.9% vs. 1.5%, p = 0.02). T1b patients without BCG induction had worse RFS and PFS (all p ≤ 0.02) compared to T1a, while no differences were observed in patients who received complete BCG induction. At Multivariate analysis, completing at least a BCG induction course was associated with better outcomes across all endpoints.

CONCLUSIONS

Invasion of the MM in primary T1 NMIBC is associated with a higher risk of upstaging to MIBC. Patients who received full BCG induction had similar outcomes regardless of substaging, whereas T1b patients without BCG induction experienced higher recurrence and progression rates.