CD274 and melanoma: Programmed cell death 1 ligand 1 (PD-L1; also known as B7-H1 or CD274), a 40-kDa transmembrane protein belonging to the B7 family that negatively regulates T-cell signaling, is frequently upregulated in a number of different tumors, including melanoma, ovarian, lung, glioblastoma, breast, and pancreatic cancers [13-17].