STAT1 and neoplasm: To evaluate the potential roles of STAT1 and/or STAT3 activation in mediating PD-L1 protein expression, 31 tumor cell lines (16 MELs, 12 RCCs, 3 SCCHNs) were treated with IFN-g or IL-6, a prototypical STAT3 activator, and then assessed for STAT1 and STAT3 phosphorylation by Western blotting.