CD274 and neoplasm: PD-L1 expression in tumor cells is the first possible biomarker, and it was reported to be regulated by two main pathways: (1) Adaptive immune tolerance mainly depends on some specific cytokines, such as interferon (IFN)-γ, granulocyte-macrophage colony-stimulating factor (GM-CSF), and interleukin (IL)-4 (20).