In an open-label , international , multicentre expansion cohort of a phase 1 trial , patients ( aged 18 years ) with advanced melanoma whose disease had progressed after at least two ipilimumab doses were randomly assigned with a computer-generated allocation schedule ( 1:1 final ratio ) to intravenous pembrolizumab at 2 mg/kg every 3 weeks or 10 mg/kg every 3 weeks until disease progression , intolerable toxicity , or consent withdrawal .