We did a multicentre , randomised , double-blind , phase 3 trial in which men with at least one bone metastasis from castration-resistant prostate cancer that had progressed after docetaxel treatment were randomly assigned in a 1:1 ratio to receive bone-directed radiotherapy ( 8 Gy in one fraction ) followed by either ipilimumab 10 mg/kg or placebo every 3 weeks for up to four doses .