In patients with tumors positive for the PD-1 ligand ( PD-L1 ) , the median progression-free survival was 14.0 months in the nivolumab-plus-ipilimumab group and in the nivolumab group , but in patients with PD-L1-negative tumors , progression-free survival was longer with the combination therapy than with nivolumab alone ( 11.2 months [ 95 % CI , 8.0 to not reached ] vs. 5.3 months [ 95 % CI , 2.8 to 7.1 ] ) .