This phase II multicentric-study analyse the role of the steroid switch in patients receiving AA. Previous retrospective data (Lorente et al, BJC 2014) has shown that the change of prednisone by dexamethasone in CRPC patients treated with AA post-docetaxel leaded to durable biochemical responses in 40% of cases. Recently, superiority of dexamethasone over prednisone in PSA response has been reported by a phase II trial that included 82 chemotherapy-naive metastatic CRPC patients.