CD274 and cancer: Previously published studies suggest that tumor PD-L1 protein expression may be evaluated on human cancers using immunohistochemistry (IHC) in FFPE samples [6, 26]; however, several factors may impact the evaluation of PD-L1 positivity by conventional IHC, such as the specificity and reproducibility of the commercially available antibodies as well as the subjectivity of the staining interpretation.