PDCD1 and neoplasm: The anti-programmed-cell-death-protein-1 (PD-1) monoclonal antibodies nivolumab and pembrolizumab promote tumour cell destruction by inhibiting the PD-1 ligand (PD-L1) expressed on tumour cells to be recognised as self by the immune system, while ipilimumab is a monoclonal antibody that blocks the cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), a receptor on the T cell surface that inhibits the inappropriate or prolonged activation of T cells [16,17,20,21].