PDCD1 and cancer: Immune escape is a major contributing factor to the malignant progression of cancer, which was regulated by the disturbance of cell immune function (e.g., decreased immunological activated cells and immunosuppressive cells), and overexpression of immune checkpoint genes including programmed cell death-1 (PD-1), cytotoxic T lymphocyte antigen 4 (CTLA-4), and lymphocyte-activation gene 3 (LAG3) in TME [60, 61].