In this randomised , double-blind , placebo-controlled , phase 3 study , we randomly assigned chemotherapy-naive patients with progressive metastatic castration-resistant prostate cancer in a 1:1 ratio to receive docetaxel ( 75 mg/m ( 2 ) ) on day 1 and prednisone ( 5 mg twice daily ) on days 1-21 and either lenalidomide ( 25 mg ) or placebo once daily on days 1-14 of each 21 day treatment cycle .