Radium-223 is approved by the US Food and Drug Administration and European Medicines Agency for the treatment of metastatic castration-resistant prostate cancer (mCRPC). There are currently no markers for selecting patients most likely to complete radium-223 treatment.

In this phase IIIb, international, single-arm study, patients received radium-223, 55 kBq/kg, every 4 weeks for ≤6 cycles. Primary end points were safety and overall survival. In post hoc analyses patients were grouped according to number of radium-223 injections received (1-4 or 5-6). Associations between baseline covariates and number of injections were investigated.

Of 696 eligible patients, 473 (68%) had received 5 to 6 radium-223 injections and 223 (32%) 1 to 4 injections. Patients with less pain (moderate-severe vs. none-mild, odds ratio [OR], 0.41; P < .0001), lower Eastern Cooperative Oncology Group performance status (≥2 vs. 0-1, OR, 0.51; P = .0074), lower prostate-specific antigen level (>141 μg/L vs. ≤141 μg/L, OR, 0.40; P < .0001), and higher hemoglobin level (<10 g/dL vs. ≥10 g/dL, OR, 0.50; P = .0206) were more likely to receive 5 to 6 than 1 to 4 injections. Median overall survival was not reached and was 6.3 months (95% confidence interval, 5.4-7.4) in patients who had received 5 to 6 and 1 to 4 radium-223 injections, respectively. Adverse events were less common in patients who received 5 to 6 than 1 to 4 injections; anemia was reported in 87 (18%) and 64 (29%) patients, respectively.

Patients with less advanced mCRPC are more likely to receive 5 to 6 radium-223 injections and to achieve better overall survival. Consideration of baseline and disease characteristics is recommended before initiation of radium-223 treatment.

Clinical genitourinary cancer. 2019 May 31 [Epub ahead of print]

Fred Saad, Silke Gillessen, Daniel Heinrich, Daniel Keizman, Joe M O’Sullivan, Sten Nilsson, Kurt Miller, Manfred Wirth, John Reeves, Monica Seger, Joan Carles, Axel Heidenreich

Department of Urology, University of Montreal Hospital Center, Montreal, Quebec, Canada. Electronic address: ., Division of Cancer Sciences, University of Manchester and The Christie Hospital, Manchester, United Kingdom and Kantonsspital St Gallen, Division of Oncology/Haematology and University of Bern, Switzerland., Department of Oncology, Akershus University Hospital, Lørenskog, Norway., Genitourinary Oncology Service, Institute of Oncology, Meir Medical Center, Kfar-Saba, Israel., Department of Clinical Oncology, The Centre for Cancer Research and Cell Biology, Queen’s University Belfast and the Northern Ireland Cancer Centre, Belfast, Northern Ireland., Department of Oncology, Karolinska University Hospital, Stockholm, Sweden., Department of Urology, Charité University Medicine Berlin, Berlin, Germany., Department of Urology, University Hospital Carl-Gustav Carus, Dresden, Germany., Pharmaceutical Division of Bayer, Whippany, NJ., Department of Medical Oncology, Vall d’Hebron University Hospital, Vall d’Hebron Institute of Oncology, Barcelona, Spain., Department of Urology, University Hospital Cologne, Cologne, Germany.