Immune checkpoint inhibitors (ICIs), which target immune checkpoint regulators such as programmed cell death protein 1 (PD-1), its ligand PD-L1, or cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), have emerged as a promising alternative by enhancing the activation and proliferation of tumor-specific T cells. The gene discussed is PDCD1; the disease is neoplasm.