PDCD1 and cancer: Inhibitory immune checkpoint pathways have been widely studied as possible mechanisms of immune escape in cancer, and for some of them, particularly the cytotoxic T lymphocyte antigen 4 (CTLA-4), and the programmed cell death-1 (PD1) pathways, inhibitory antibodies (Abs) have garnered approval worldwide for the treatment of a broad spectrum of neoplastic diseases [6].