TIGIT and neoplasm: Immunohistochemical as well as mRNA expression analyses of the immune “microenvironment” have shown that the majority of PDS represent inflammatory and immunogenic tumors with a high number of CD8+ tumor-infiltrating lymphocytes (TILs) and expression of diverse checkpoint molecules such as PD-L1, TIGIT, LAG-3, and CTLA-4 (2, 15, 16).