PDCD1 and neoplasm: During cancer progression, tumor cells employ diverse strategies to escape immune surveillance by, for example, overexpressing programmed death ligand 1 (PD-L1; cluster of differentiation 274, CD274), which binds programmed cell death protein 1 (PD-1, PDCD1) on the surface of cytotoxic CD8+ T cells and attenuates their anti-tumor activity [1].