It is known that Programmed Cell Death Protein 1 (PD-1) is highly expressed in Tumor-Infiltrating Lymphocytes (TILs) and that PD-1 Ligands (especially PD-L1) and Cytotoxic T Lymphocyte Associated protein 4 (CTLA-4) can be expressed in many cancerous cell types. Here, PDCD1 is linked to neoplasm.