CD274 and Merkel cell skin cancer: Regarding MCC, while MCPyV status [17,18,19,186] and PD-L1+ expression (≥1%, evaluated with immunohistochemistry) [17,18,19,20,83] cannot be considered useful predictors of response, PD-1 and PD-L1 density, PD-L1/PD-1 proximity [197], and features of TILs TCR repertoire (with low clonality and high diversity) [19,195] are associated with good outcomes.