CD274 and neoplasm: The expression of programmed cell death ligand 1 (PD-L1), an important immunosuppressive protein on the surface of tumor cells, is regulated at multiple levels, including genomic alterations (amplification or translocation), epigenetic modifications (methylation of histones or CpG islands and histone acetylation), transcriptional regulation (inflammatory stimulation and oncogenic signaling), post-transcriptional regulation (miRNA, 3’-UTR, RAS and angiotensin II status regulation), post-translational modifications (ubiquitination, glycosylation, phosphorylation and palmitoylation) (7).