PDCD1 and neoplasm: Different studies have highlighted the importance of the programmed cell death-1 (PD-1)/programmed cell death ligand-1 (PD-L1) pathway controlling inflammation degree to prevent an exacerbated immune response in tumor growth, in which PD-L1 expressed on tumor cells can inhibit the effector functions of CD8+ T cells, leading to the progression of tumors (41).