CD274 and neoplasm: Several factors may explain the heterogeneity of the predictive values for the PD-L1 expression, including differences in the PD-L1 IHC assay platforms and detection antibodies, differing IHC cutoffs, tissue preparation, processing variability, primary versus metastatic lesions, oncogenic versus induced PD-L1 expression, and the staining of tumor versus immune cells [42,47,75,87,88].