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Effect of radium-223 dichloride on symptomatic skeletal events in patients with castration-resistant prostate cancer and bone metastases: results from a phase 3, double-blind, randomised trial.

Sartor O, Coleman R, Nilsson S, Heinrich D, Helle SI, O'Sullivan JM, Fosså SD, Chodacki A, Wiechno P, Logue J, Widmark A, Johannessen DC, Hoskin P, James ND, Solberg A, Syndikus I, Vogelzang NJ, O'Bryan-Tear CG, Shan M, Bruland ØS, Parker C.

Lancet Oncol 2014 Jun;15(7):738-46.

Abstract:

BACKGROUND: Bone metastases frequently cause skeletal events in patients with metastatic castration-resistant prostate cancer. Radium-223 dichloride (radium-223) selectively targets bone metastases with high-energy, short-range α-particles. We assessed the effect of radium-223 compared with placebo in patients with castration-resistant prostate cancer and bone metastases.

METHODS: In this phase 3, double-blind, randomised ALSYMPCA trial, we enrolled patients who had symptomatic castration-resistant prostate cancer with two or more bone metastases and no known visceral metastases, who were receiving best standard of care, and had previously either received or were unsuitable for docetaxel. Patients were stratified by previous docetaxel use, baseline total alkaline phosphatase level, and current bisphosphonate use, then randomly assigned (2:1) to receive either six intravenous injections of radium-223 (50 kBq/kg) or matching placebo; one injection was given every 4 weeks. Randomisation was done with an interactive voice response system, taking into account trial stratification factors. Participants and investigators were masked to treatment assignment. The primary endpoint was overall survival, which has been reported previously. Here we report on time to first symptomatic skeletal event, defined as the use of external beam radiation to relieve bone pain, or occurrence of a new symptomatic pathological fracture (vertebral or non-verterbal), or occurence of spinal cord compression, or tumour-related orthopeadic surgical intervention. All events were required to be clinically apparent and were not assessed by periodic radiological review. Statistical analyses of symptomatic skeletal events were based on the intention-to-treat population. The study has been completed and is registered with ClinicalTrials.gov, number NCT00699751.

FINDINGS: Between June 12, 2008, and Feb 1, 2011, 921 patients were enrolled, of whom 614 (67%) were randomly assigned to receive radium-223 and 307 (33%) placebo. Symptomatic skeletal events occurred in 202 (33%) of 614 patients in the radium-223 group and 116 (38%) of 307 patients in the placebo group. Time to first symptomatic skeletal event was longer with radium-223 than with placebo (median 15·6 months [95% CI 13·5-18·0] vs 9·8 months [7·3-23·7]; hazard ratio [HR]=0·66, 95% CI 0·52-0·83; p=0·00037). The risks of external beam radiation therapy for bone pain (HR 0·67, 95% CI 0·53-0·85) and spinal cord compression (HR=0·52, 95% CI 0·29-0·93) were reduced with radium-233 compared with placebo. Radium-223 treatment did not seem to significantly reduce the risk of symptomatic pathological bone fracture (HR 0·62, 95% CI 0·35-1·09), or the need for tumour-related orthopaedic surgical intervention (HR 0·72, 95% CI 0·28-1·82).

INTERPRETATION: Radium-223 should be considered as a treatment option for patients with castration-resistant prostate cancer and symptomatic bone metastases.

FUNDING: Algeta and Bayer HealthCare Pharmaceuticals.

Copyright © 2014 Elsevier Ltd. All rights reserved.

Comment from Henk van der Poel: The ALSYMPCA trial showed an median overall survival benefit of 3.6 months in men with castration resistant prostate cancer. In the publication by Sartor et al., the skeletal related events were studied as an endpoint. Six times Rad223 infusion was shown to reduce the need of external beam radiotherapy for painful bone metastases, and the presence of spinal cord compression, but not symptomatic pathological fractures and tumor-related orthotopic surgery. Median overall time to first SRE was delayed by 6.6 months in the Rad223 group compared to placebo. This is longer than shown in studies comparing placebo and denosumab of zoledronic acid. Interestingly, the benefit of Rad223 for preventing SRE is most marked in patients with earlier docetaxel use or bisphosphonate use at study entry. The relatively mild toxicity profile and limited interval of use (6 months) render Rad223 an interesting agent not only to improve survival but also decrease the burden of skeletal related events, in particular spinal cord compression, in men with CRPC.

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