All but one study assessed PD-L1 expression by immunohistochemistry (IHC), nevertheless there was a variety of criteria for PD-L1 positivity on tumor cells: most studies addressed the proportion of tumor cells with membrane staining, with cut-off values ranging from ≥ 1 to ≥ 25%; 6 studies used criteria based on immune reactive score (IRS) [43, 51, 64, 66, 76, 77]; and 5 integrated PD-L1 staining on immune cells on their positivity criteria (for example, by determining the CPS) [42, 46, 48, 49, 68]. This evidence concerns the gene CD274 and neoplasm.