PDCD1 and cancer: Programmed cell death protein-1 (PD-1), a member of the CD28 family of proteins, is mainly expressed on T-cell surface [1] and its ligand, programmed cell death ligand-1 (PD-L1), is frequently overexpressed in many types of human cancers, including non-small-cell lung cancer (NSCLC), and is associated with a poor prognosis [2].