Current evidence suggests that tumor-associated macrophages (TAMs) account for the majority of infiltrating immune cells in tumor tissue [13,14] and orchestrate the formation of the immunosuppressive environment by recruiting T regulatory cells (Tregs) and Myeloid-derived suppressor cells (MDSCs), secreting inhibitory cytokines, inducing hyper-expression of PD-L1, which is the ligand of programmed cell death protein 1 (PD-1) of T cells and altering the metabolic profile of immune cells [13,15]. The gene discussed is PDCD1; the disease is neoplasm.