EGFR and neoplasm: While we have previously reported a similar correlation between FLT and epidermal growth factor receptor (EGFR) expression (39), the quantification of PD-L1 expression is far more challenging due to the generally low tumor expression levels, considerable intra- and inter-tumoral heterogeneity of PD-L1 expression, and a ubiquitous presence of PD-L1 in normal lymphoid organs (24, 64).