Mixed low- and high-grade non-muscle-invasive bladder cancer: a histological subtype with favorable outcome.

OBJECTIVE: To determine whether heterogeneity of tumor grade affects the response to Bacillus Calmette-Guérin (BCG) treatment for patients with non-muscle-invasive bladder cancer (NMIBC).

METHODS: Patients with Ta or T1 NMBIC receiving a 6-week induction course of intravesical BCG therapy after transurethral resection were divided according to the tumor grade. Clinical and pathological variables were compared. Advanced intervention-free survival (AIFS), defined as duration of freedom from advanced intervention (including non-BCG intravesical agents or cystectomy) or metastasis, was plotted using Kaplan-Meier methods. The effect of grade on survival duration was assessed by multivariate Cox proportional hazards modeling.

RESULTS: One hundred and fifty-three patients were identified: 17 with mixed low- and high-grade (MG) and 136 with pure high-grade (PHG) NMIBC. Demographic and additional pathologic variables were comparable between groups (p > 0.05). Five-year AIFS was 88.2% for MG patients, compared to 48.5% for PHG patients (p = 0.030 by log-rank test). On multivariate analysis, PHG was an independent risk factor for worse AIFS (HR 4.4, 95% CI 1.1-18.4, p = 0.040). Among patients failing to respond to primary BCG induction, who underwent a secondary induction of BCG with interferon, MG patients had better response than PHG patients (100 vs. 26.3%, p = 0.035).

CONCLUSIONS: Mixed low- and high-grade NMIBC exhibits a significantly better response profile to intravesical BCG therapy compared to PHG NMIBC. The implications of these results are that less aggressive treatment strategies for this unique cancer entity may be needed and that there is a benefit to the reporting of tumor heterogeneity in transurethral resection of bladder tumor specimens.