PDCD1 and neoplasm: These tumors present tumor-infiltrating lymphocytes (TILs) with a strong expression of CD8 and the immunological markers Programmed Cell Death Protein-1 (PD-1) and its ligand (PD-L1) [44, 45] Patients with SSC of the anal canal with high levels of infiltration of TILs present a relapse-free rate higher than those with low levels of infiltration of TILs [46].