PDCD1 and cancer: The activation of cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), programmed cell death protein 1 (PD-1), and programmed death-ligand 1 (PD-L1) impairs the ability of T Cells to activate, recognize, and eliminate cancer cells, thereby bypassing anti-tumor immune surveillance and consequently diminishing the therapeutic efficacy of RT (Zhang et al., 2021).