The median progression-free survival was 11.5 months ( 95 % confidence interval [ CI ] , 8.9 to 16.7 ) with nivolumab plus ipilimumab , as compared with 2.9 months ( 95 % CI , 2.8 to 3.4 ) with ipilimumab ( hazard ratio for death or disease progression , 0.42 ; 99.5 % CI , 0.31 to 0.57 ; P < 0.001 ) , and 6.9 months ( 95 % CI , 4.3 to 9.5 ) with nivolumab ( hazard ratio for the comparison with ipilimumab , 0.57 ; 99.5 % CI , 0.43 to 0.76 ; P < 0.001 ) .