CD274 and neoplasm: This is a challenging task due to: poorly circumscribed and/or heterogeneous tumours; the intra-tumoural heterogeneity of PD-L1; and pre-analytical variables that affect tissue such as fixation time, endogenous and exogenous pigments within the tissue, staining expression in other tissue compartments (stromal and inflammatory cells), and misinterpretation in IHC evaluation (staining of necrosis or cytoplasmic staining artefact) [144,146].