In patients with tumors positive for the PD-@ ligand ( PD-L@ ) , the median progression-free survival was @ months in the nivolumab-plus-ipilimumab group and in the nivolumab group , but in patients with PD-L@-negative tumors , progression-free survival was longer with the combination therapy than with nivolumab alone ( @ months -LSB- @ % CI , @ to not reached -RSB- vs. @ months -LSB- @ % CI , @ to @ -RSB- ) .