Sequencing of Radium-223 and Docetaxel in Symptomatic Bone-only Metastatic Castration-resistant Prostate Cancer

Randomized, multicentre phase II trial of the sequencing of Radium-223 and Docetaxel plus prednisone in symptomatic bone-only metastatic castration-resistant prostate cancer (mCRPC) Primary objective: To determine the effects of sequential treatment between radium-223 and docetaxel on the percentage of symptomatic bone-only CRPC patients experiencing improvement or worsening in health-related quality of life (HRQoL) Secondary objective: To compare survival in patients treated with sequential therapy between radium-223 and docetaxel and to identify predictive factors of Radium-223 for clinical outcome (progression free survival and overall survival) in this patient population. Study Treatment: Radium-223: administered at the dose of 55 kBq per kg body weight, given at 4 week intervals for 6 injections, by slow intravenous injection. Docetaxel: administered at the dose of 75 mg/m2 by intravenous infusion over a period of 1 hour every 3 weeks for 10 cycles. It is associated with prednisone 5 mg orally twice daily administered continuously. Statistical methodology A responder analysis investigating treatment effects on percentage of patients experiencing meaningful HRQoL improvement/worsening on treatment will be conducted. When defining meaningful improvement/worsening, the upper limit of the minimally important difference (MID) range will be used. The MIDs for FACT-P total score and subscales that will be used in this study will be 10 and 3, respectively. Patients experiencing a QoL increase \>=MID from baseline at week 12 will be considered responders while patients experiencing a decrease in HRQoL score \>=MID at this time point will be considered to have experienced worsening HRQoL. According to primary endpoint, considering a type I error 0.10, type II error 0.20, proportion of responder patients in the standard arm 0.10 and in the experimental arm of 0.40, a total of 70 patients (35 for each arm) will be enrolled in the study. Chi-square tests will be used to test for an association between treatment and meaningful improvement (i.e. responder) or worsening in HRQoL. According to secondary endpoints, PFS, TPFS and OS will be estimated by the Kaplan-Meier method. The treatment groups will be compared with a two-sided log rank test. All analyses will be done in the intention-to-treat population. For translational studies, we will conduct a prognostic and predictive factor analysis for time-to-event clinical outcomes using a univariate Cox model; significant factors subsequently will be included in a multivariable Cox regression model (cutoff p\<0•05).