The randomized , double-blind phase III AFFIRM trial demonstrated that enzalutamide , an oral androgen receptor inhibitor , significantly prolonged overall survival ( OS ) -LSB- median @ versus @ months ( hazard ratio , HR ) @ ( @ % confidence interval , CI , @-@ @ ) ; P < @ -RSB- compared with placebo in patients with metastatic castration-resistant prostate cancer who received prior docetaxel chemotherapy .