CD274 and melanoma: Six trials evaluated the combination of anti-PD-1/PD-L1 drugs with ipilimumab [29, 38] and chemotherapy [36, 42–44] compared with conventional treatment; seventeen trials assessed the efficacy of anti-PD-1/PD-L1 monotherapies [22–28, 30–35, 37, 39–41]; one trial, namely, CheckMate 067 [19], was purposed to evaluate the therapeutic effect of nivolumab monotherapy or combination therapy with nivolumab plus ipilimumab in melanoma compared with ipilimumab.