STAT3 and gastric cancer: Studies have reported overexpression of PD-L1 mRNA and protein in EBV-driven malignant tumors, such as EBV-associated gastric cancer, Hodgkin's lymphoma and EBV-peripheral T-cell lymphoma, mediated by interferon gamma (IFN-γ), mitogen activated protein kinase (MAPK), nuclear factor kappa B (NF-κB), and signal transducer and activator of transcription 3 (STAT3) signaling pathways [13, 14, 37–40].