PDCD1 and cancer: Novel therapy targeting immune checkpoints, such as programmed cell death 1 (PD1)/programmed cell death 1 ligand 1 (PD-L1), cytotoxic T-lymphocyte associated protein 4 (CTLA4) and T-cell membrane protein 3 (TIM3) have made breakthrough in many types of cancer treatment (Sharma and Allison, 2015; Topalian et al., 2016).