STAT3 and melanoma: This was based on its role in promoting PD-L1 expression downstream of IFNγ in melanoma [9], the correlation between STAT3 and PD-L1 mRNA levels (Supplementary Figure S3B), the fact that STAT3 can interact with HIF1 [18, 26], and has been reported to cooperate with HIF1 on the stimulation of PD-L1 expression in colon cancer cells [27], and in hypoxic NSCLC cells [18].