PDCD1 and prostate cancer: Although prostate cancer is generally classified as an immunologically “cold” tumor demonstrating a poor response to conventional immunotherapeutic approaches, PD-1/PD-L1 inhibitors manifest significant antitumor activity through three distinct mechanisms: (1) blockade of T-cell inhibitory signaling pathways, (2) enhancement of T-cell activation, and (3) reduction of tumor immune evasion.