Mistletoe Plant Extract in Patients with Nonmuscle Invasive Bladder Cancer: Results of a Phase Ib/IIa Single Group Dose Escalation Study

PurposeWe determined the maximum tolerated dose, safety and effectiveness of intravesical instillation of mistletoe extract after transurethral resection of nonmuscle invasive bladder cancer.Materials and MethodsIn this single group dose escalation study patients with nonmuscle invasive bladder cancer were treated with weekly instillations of mistletoe extract for 6 weeks. Four weeks before instillation therapy all patients underwent transurethral resection of bladder tumors. During this procedure a marker tumor was left. At 12 weeks after the start of instillation therapy transurethral resection of the marker tumor or biopsy of the former marker tumor location was done so that patients were tumor free when entering followup until week 48. During the followup clinical assessment laboratory tests for safety and cystoscopy were done every 12 weeks.ResultsA total of 36 patients were treated with increasing doses of mistletoe extract. We found no dose limiting toxicity up to a dose of 675 mg of plant extract. Besides local reactions we saw hints that pyrexia may develop. All adverse events were well manageable. At 12 weeks a marker tumor remission rate of 55.6% (95% CI 38.1 to 72.1) was achieved. At 1 year a recurrence rate of 26.3% (95% CI 9.1 to 51.2) was observed.ConclusionsIn this study intravesical instillation of mistletoe extract as treatment in patients with nonmuscle invasive bladder cancer was shown to be safe and well tolerated. Promising data on efficacy were observed and will be further investigated in a phase III study.