PDCD1 and neoplasm: Further studies that comprise not only the overall-evaluation of TILs and the degree of PD-L1 expression on tumor and immune cells but also include the differential analysis of PD-1 expression on immune cell subpopulations (i.e., NK-, dendritic, CD4- and CD8-positive T-cells, and monocytes) will specify and thus considerably enhance the diagnostic and prognostic significance of immune cell analyses [24].