Preliminary results of RTOG 0831, a randomized, double-blinded, placebo-controlled trial of tadalafil in the prevention of erectile dysfunction in patients treated with radiotherapy for prostate cancer.

Abstract

9525 Background: Determine if prophylactic tadalafil maintains spontaneous (off-drug) erectile function (EF) compared to placebo in patients (pts) treated with radiotherapy (RT) for prostate cancer. Methods: Double-blind 1:1 randomization to tadalafil 5mg daily for 6 mos vs placebo starting with RT. Primary outcomes measured by International Index of Erectile Function (IIEF). Eligibility included pre-RT IIEF Question [Q] 1 response “sometimes/most times/always” able to get an erection. Ps treated with hormones were excluded. Primary outcome was response to IIEF Q1 at 30 wks (6 wks off drug). Pts were stratified by RT modality (external vs. brachytherapy) and age (≤65 vs. >65 years). 182 pts were needed in an intent-to-treat analysis to show a difference from 20% responders with placebo to 40% with tadalafil based on a 2-sided Fishers exact test with α=0.05 and 80% power. Results: We report on 155/222 analyzable/eligible pts. Median age was 63 years, white (73%), and external RT (63%). Mean total dose for external RT was 77.23 Gy and 136.74 Gy for brachytherapy with penile bulb D50 of 24.46 Gy and 31.24 Gy respectively. Most pts completed treatment per protocol (84% tadalafil, 70% placebo). Spontaneous EF at 30 wks from drug start was not different (p=0.99) between arms based on IIEF Q1 response, total IIEF score (52.5 drug vs 52.8 placebo), or score change from baseline (-8.0 drug vs -8.8 placebo). No difference in these outcomes was noted at 1 year. Non-responders at 30 wks were likely to be older (age≥65; p=0.432), but there were no significant predictors at 1 year. About 80% of pts maintained spontaneous EF in both arms. Conclusions: Low-dose daily tadalafil did not preserve EF within the first year of RT for prostate cancer. If tadalafil positively influences delayed RT-induced vasogenic injury, additional time may be needed to observe a benefit to tadalafil as a preventive agent. Alternatively, tadalafil dose modification or altered dosing schedules may be needed to demonstrate a protective effect of this agent when used with RT. Clinical trial information: NCT00951184.