An immediate, single intravesical instillation of mitomycin C is of benefit in patients with non–muscle-invasive bladder cancer irrespective of prognostic risk groups

Background: In a recent meta-analysis, subgroups of patients were defined that may not benefit from a single, immediate instillation with chemotherapy. This led to a change in the European Association of Urology bladder cancer guidelines. In a previous paper, our group confirmed the efficacy of an immediate instillation of mitomycin C (MMC). However, prognostic groups in that study differ from those in the meta-analysis. Therefore, we performed a reanalysis using contemporary risk groups. Objectives: To validate whether specific subgroups of patients with non–muscle-invasive bladder cancer (NMIBC) benefit from an immediate instillation with MMC. Patients and methods: All 2,243 NMIBC patients enrolled in our randomized controlled trial between 1998 and 2003 were analyzed. Treatment effect was investigated for all subgroups, including subgroups that did not benefit from an immediate instillation according to the meta-analysis. Time to recurrence was assessed using Kaplan-Meier curves and multivariable Cox regression. Differences in treatment effect between subgroups was tested using the variable treatment by covariate interactions in a Cox regression model. Results: The difference in time to recurrence was statistically significant in favor of an immediate instillation with MMC (P < 0.001) which corresponds to a 25% risk reduction (hazard ratio: 0.75, 95% confidence interval, 0.64–0.88, P < 0.001). Treatment effect of an immediate instillation with MMC did not differ significantly between any of the subgroups. Conclusions: In contrast to the recommendations in the European Association of Urology guidelines, we could not identify any subgroup of patients with NMIBC who do not benefit from an immediate instillation with MMC after transurethral resection.