PDCD1 and neoplasm: Immune checkpoint inhibitors (such as ipilimumab, nivolumab and pembrolizumab) are novel monoclonal antibodies that target cytotoxic T-lymphocyte–associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1) cell signaling, respectively and attempt to restore patients’ anti-tumor T-cell response that may be endogenously diminished as part of tumor escape mechanisms.