Purpose In recent years some reports have suggested without any significant evidence that mitomycin C instillation would be more effective with urinary alkalinization. We investigated the association between urinary pH and the efficiency of mitomycin C instillation. Materials and Methods We identified 130 patients treated with transurethral resection of a bladder tumor and adjuvant intravesical mitomycin C instillation between 1985 and 2008 at Keio University Hospital. Urinary pH was determined in 124 of the 130 patients just before mitomycin C administration during the scheduled instillation period. These 124 patients were assigned to groups according to urinary pH in increments of 0.5 and the association between urinary pH and clinicopathological characteristics was evaluated. Results Mean ± SD urinary pH was 5.77 ± 0.05 (range 5.00 to 7.66) during the scheduled instillation period. Urinary pH was 5.00 to 5.49, 5.50 to 5.99, 6.00 to 6.49, 6.50 to 6.99 and 7.00 in 39, 46, 25, 7 and 7 patients, respectively. Patients were further divided into 2 groups by urinary pH using a cutoff of 5.5, including 39 with pH less than 5.5 and 85 with pH 5.5 or more. Age, gender, tumor grade, primary/recurrent disease, pathological stage and the presence or absence of concomitant carcinoma in situ were not significantly difference between the 2 groups. Multivariate analysis revealed that categorical urinary pH was an independent risk factor for tumor recurrence (HR 1.75, p = 0.032). Three and 5-year recurrence-free rates were 64.2% and 52.9% in patients with pH 5.5 or greater, and 41.9% and 38.4% in those with pH less than 5.5, respectively (p = 0.046). Multivariate analysis showed that the HR of urinary pH for tumor recurrence was 1.84 and 2.54 at the 5.4 and 5.2 cutoffs, respectively. Conclusions Results suggest that urinary pH more than 5.5 is associated with a decreased risk of tumor recurrence in patients treated with intravesical mitomycin C for nonmuscle invasive bladder cancer. Monitoring urinary pH during mitomycin C adjuvant treatment and modifying pH for urine alkalization may improve the therapeutic efficacy of mitomycin C instillation.
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