PDCD1 and neoplasm: In recent years, a deep understanding of the mechanism underlying tumor immune escape (33) has resulted in the development of several immunotherapies (Figure 1), Since the development of the first tumor immunotherapy drug interferon (IFN)-α, several immunotherapy drugs, such as immune checkpoint (PD-1/PD-L1, CLTA-4, etc.)inhibitors, CAR T cell therapy, tumor vaccine, and oncolytic viruses, have been approved because of their good therapeutic effects.