In this double-blind study involving @ patients with metastatic melanoma who had not previously received treatment , we randomly assigned patients in a @:@ ratio to receive ipilimumab ( @ mg per kilogram of body weight ) combined with either nivolumab ( @ mg per kilogram ) or placebo once every @ weeks for four doses , followed by nivolumab ( @ mg per kilogram ) or placebo every @ weeks until the occurrence of disease progression or unacceptable toxic effects .