The median overall survival was 12.2 months ( 95 % confidence interval [ CI ] , 9.7 to 15.0 ) among 292 patients in the nivolumab group and 9.4 months ( 95 % CI , 8.1 to 10.7 ) among 290 patients in the docetaxel group ( hazard ratio for death , 0.73 ; 96 % CI , 0.59 to 0.89 ; P = 0.002 ) .