The use of intermittent enzalutamide dosing in the treatment of metastatic castrate-resistant prostate cancer.

Abstract

81 Background: Intermittent hormone manipulation in castrate-sensitive prostate cancer can improve quality of life whilst maintaining comparable disease outcomes with continuous scheduling. Enzalutamide is effective in metastatic castrate-resistant prostate cancer (mCRPC) treatment but can have significant side-effects. We conducted a retrospective analysis of patients treated with intermittent enzalutamide compared with continuous dosing. Methods: Patients prescribed enzalutamide for mCRPC at Royal Cornwall Hospital from September 2011 to February 2018 were included. Data was collected from electronic medical records, selecting patients with at least a 1 month treatment break. Kaplan-Meier analysis of overall survival from enzalutamide start (OS), time to PSA failure (TTF) and total enzalutamide treatment time (TTT) was calculated for intermittent and continuous responders (>50% PSA drop), assigned significance level of 0.05. Results: 243 patients received enzalutamide, 110 (45%) were continuous responders and 29 (12%) had intermittent dosing. All patients treated intermittently had a PSA response prior to first treatment break, which was most commonly for fatigue (60%). 25% were still receiving enzalutamide. Median number of breaks was 1 (range 1-7), time on treatment was 70% and time to first break was 5 months. The intermittent group had significantly improved OS with median not reached, median OS for continuous responders was 19 months (HR 2.39, 95% CI 1.53-3.76, p=0.002). The intermittent group had prolonged TTF (median 13 vs 6 months, p=0.001) and TTT (median 30 vs 10 months, p=0.0003). Conclusions: Intermittent dosing of enzalutamide in these mCRPC patients does not adversely impact OS, increasing time patients remain on treatment. However, this was a small, retrospective, single-centre study; prospective trials are necessary to clarify the role of intermittent enzalutamide.[Table: see text]