In this randomised , double-blind , placebo-controlled , phase @ study , we randomly assigned chemotherapy-naive patients with progressive metastatic castration-resistant prostate cancer in a @:@ ratio to receive docetaxel ( @ mg/m ( @ ) ) on day @ and prednisone ( @ mg twice daily ) on days @-@ and either lenalidomide ( @ mg ) or placebo once daily on days @-@ of each @ day treatment cycle .