Main reasons are different assays used (SP142, SP263, and 22C3 assays), absence of a unified scoring system [IC-tumor-infiltrating immune cells, TPS-tumor proportion score vs. CPS-combined positive score, that is the number of PD-L1 staining cells (tumor cells, lymphocytes, macrophages) divided by the total number of viable tumor cells, multiplied by 100], spatial heterogeneity of the tumor itself as well as the reliability of IHC-based detection of PD-L1 positivity [31]. This evidence concerns the gene CD274 and neoplasm.