CD274 and neoplasm: The classification is based on the expression of PD-L1 and tumor-infiltrating lymphocytes (TILs) and consists of four types as follows: type I (PD-L1+/TILHigh, adaptive immune resistance), type II (PD-L1−/TILLow, immune ignorance type), type III (PD-L1+/TILLow, intrinsic induction of PD-L1 in the absence of TILs), and type IV (PD-L1−/TILHigh, components other than PD-L1 suppressing the action of TILs) [11].