Disease characteristics and completion of treatment in patients with metastatic castration-resistant prostate cancer treated with radium-223 in an international early access program

Abstract

BACKGROUND: 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. PATIENTS AND METHODS: 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. RESULTS: 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 Oncol.ogy Group performance status (>/=2 vS 0-1, OR, 0.51; P = .0074), lower prostate-specific antigen level (>141 mug/L vS </=141 mug/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. CONCLUSION: 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.