In 2015, nivolumab was the second PD-1 inhibitor to receive US FDA approval for the treatment of patients with unresectable or metastatic melanoma based on the results of the randomised phase 3 CheckMate 037 trial, which randomly assigned 405 patients in a 2:1 ratio to receive nivolumab 3 mg/kg every 2 weeks or ICC (dacarbazine 1000 mg/m2 every 3 weeks or paclitaxel 175 mg/m2 combined with carboplatin area under the curve 6 every 3 weeks) [61]. Here, PDCD1 is linked to metastatic melanoma.