CD274 and melanoma: Correlations between methylation status and the expression of immune checkpoint molecules and its prognostic significance have been demonstrated for PD-1, PD-L1, and PD-1 ligand 2 (PD-L2) in various malignancies, among them melanoma [32,[36], [37], [38], [39], [40], [41], [42], [43], [44]].