PDCD1 and neoplasm: The antitumor response is controlled by negative feedback mechanisms performed by molecules known as ‘immune checkpoints’, both in the priming phase -including CTLA-4, LAG-3 and TIM-3- and in the effector phase -mainly programmed cell death protein 1 (PD-1), activated by ligands (PD-L1) expressed both by cells from the tumor and TME- (10).