STAT1 and neoplasm: Although our understanding of PD-L1 expression regulation is not complete, it can be determined that PD-L1 regulation mainly works through the classical type II interferon pathway JAK1/2-STAT1/3-IRF1 axis and the PD-L1 axis, and NK cells are an important source of IFN-γ in the tumor microenvironment47, 48.