PDCD1 and neoplasm: The combination of PD-1 and its ligand can activate the PI3K-Akt-mTOR pathway in tumor cells, resulting in a decrease in T effector cells and T memory cells with immunostimulatory effects and an increase in T regulatory cells (Treg) and T exhausted cells (Tex) with immunosuppressive effects, leading to immune escape of tumor cells (78).