CD274 and cancer: Since the up-regulation of PD-L1 in tumor cells seems to be a very important mechanism for immune evasion, this process can be activated by cancer cells using multiple signals such as elevated levels of transcriptional factors STAT3 and HIF-1α, oncogenic aberrant signaling pathways EGFR, MAPK, PI3k-AKT, several cytokines including IFN-γ, IFN-α, IL-2, IL-6, IL-10, IL-12, IL-15, IL-17, IL-25, IL-27, and even viral infections like EBV (Epstein–Barr virus) in the case of gastric and nasopharyngeal cancers [18].