PDCD1 and cancer: The advent of immune checkpoint inhibitors (ICIs) in cancer treatment, encompassing monoclonal antibodies directed against programmed death receptor (PD-1), programmed death receptor ligand (PD-L1), and cytotoxic T lymphocyte-associated protein 4 (CTLA-4) receptor, has heralded a transformative era in cancer therapy, drastically altering the prognosis of numerous malignancies.