FEN1 and oral cavity squamous cell carcinoma: Furthermore, it has been demonstrated that the IFN–STAT1 pathway functions as an effector of DDR components in cancer cells by inhibiting flap endonuclease-1 (FEN1), which affects human leukocyte antigen (HLA-DR) and programmed death receptor ligand 1 (PD-L1) to suppress the tumorigenesis dependent on the IFN-γ–JAK–STAT1 pathway in oral squamous cell carcinoma [221].