PDCD1 and cancer: The latest breakthroughs in comprehending the immune system’s response to cancer have culminated in the innovation of immune checkpoint inhibitors (ICPIs), such as antibodies against programmed cell death-1 (PD-1) [5,6], programmed cell death-ligand 1 (PD-L1) [7], and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) [8].