PDCD1 and neoplasm: Monoclonal antibodies targeting programmed cell death protein 1 (PD-1), programmed death ligand 1 (PD-L1), and cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), alone or in combination, show anti-tumor activity by enhancing the immune system via T-cell activity and inhibiting the inhibition of the immune system [1,2].