PDCD1 and neoplasm: ICIs, such as anti-Cytotoxic T-Lymphocyte Antigen 4 (CTLA-4) agents (e.g., ipilimumab) and, more prominently, anti-Programmed Cell Death Protein 1 (PD-1) agents (e.g., nivolumab, pembrolizumab) and their ligands (anti-PD-L1), function by releasing the brakes on the host’s immune system, thereby reactivating cytotoxic T cells to recognize and eliminate tumor cells (7, 8) (Figure 1).