A classification of tumor microenvironment has been proposed by Teng et al., who divided the tumor milieu into 4 types, according to PD-L1 expression and to the presence or absence of tumor infiltrating lymphocytes (TILs): type I (PD-L1+/TIL+), leading to adaptive immune resistance; type II (PD-L1−/TIL−), driving immune ignorance; type III (PD-L1+/TIL−), characterized by intrinsic oncogenic pathway induction; and type IV PD-L1−/TIL+, indicating the potential suppressive role of other negative modulators in enhancing immune tolerance [74]. This evidence concerns the gene CD274 and neoplasm.