ASCO GU 2018: Radium-223 Retreatment in an International, Open-label, Phase I/II Study in Patients with CRPC and Bone Metastases: 2-year Follow-up

San Francisco, CA (UroToday.com) Dr. Oliver Sartor from Tulane University presented results of a phase I/II trial assessing retreatment with Radium-223 (Rad-223) among men with CRPC and bone metastases. Ra-223 treatment is indicated for patients with CRPC and symptomatic bone metastases at a dose of 55 kBq/kg IV injections every four weeks for a total of six doses. Early results of an international, open-label, phase I/II study showed that re-treating patients with Ra-223 was well tolerated with favorable effects on disease progression. The objective of this study was to report safety and efficacy findings from a 2-year follow-up.

For this trial, 44 patients with CRPC and bone metastases who completed six initial Ra-223 injections with no disease progression in bone and later progressed were eligible for Ra-223 re-treatment (six additional Ra-223 injections), provided that hematologic parameters were adequate. No concomitant cytotoxic agents were allowed, however other concomitant agents (eg, abiraterone, enzalutamide) were allowed at investigator discretion. The primary objective of this phase I/II trial was safety. Exploratory objectives were time to radiographic bone progression, radiographic progression-free survival (rPFS), overall survival (OS), time to first symptomatic skeletal event (SSE), and SSE-free survival, all calculated from re-treatment start. Patients will be followed for safety up to seven years after their last Ra-223 dose, and an active 2-year follow-up evaluated the above noted exploratory objectives. Among the 44 patients re-treated with Ra-223, 29 (66%) completed all six subsequent injections (median number of injections was six). Subsequently, 34 (77%) patients entered active follow-up, during which no new safety concerns were noted, however one new primary malignancy was reported (basal cell carcinoma). There were no serious drug-related adverse events. Nineteen (43%) patients had an rPFS event (radiographic progression or death), and median rPFS was 9.9 months. Only 5 (11%) of 44 patients had radiographic bone progression and the median time to radiographic bone progression was not reached. The median OS, median time to first SSE and SSE-free survival were 24.4 months, 16.7 months, and 12.8 months, respectively.

Based on results of this trial, the authors concluded that re-treating CRPC bone metastatic patients with Ra-223 was well tolerated in this select patient population. There were minimal hematologic toxicities, and Ra-223 provided continued disease control in the bone at 2-year follow-up.

Speaker: Oliver Sartor, Tulane University, New Orleans, LA

Co-Authors: Daniel Heinrich, Neil Mariados, María José Méndez-Vidal, Daniel Keizman, Camilla Thellenberg Karlsson, Avivit Peer, Giuseppe Procopio, Stephen Jay Frank, Kalevi Pulkkanen, Eli Rosenbaum, Stefano Severi, Jose Manuel Trigo Perez, Lucia Trandafir, Volker Jean Wagner, Rui Li, Luke T. Nordquist

Written by: Zachary Klaassen, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre, Twitter:@zklaassen_md at the 2018 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, February 8-10, 2018 - San Francisco, CA

References:
1. Sartor O, Heinrich D, Mariados N, et al. Re-treatment with radium-223: first experience from an international, open-label, phase I/II study in patients with castration-resistant prostate cancer and bone metastases. Ann Oncol 2017;28:2464-2471.
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