The studies on flavonoids as possible suppressors of PD-L1/PD-1 immune checkpoint have not been very intense yet, nevertheless the first encouraging results were obtained demonstrating the inhibition of PD-L1 expression by flavone apigenin in A375 melanoma cells [142] and PD-1/PD-L1 inhibition in vitro by flavonols quercetin [143] and fisetin [143] as well as isoflavonoid glyasperin C [144]. This evidence concerns the gene PDCD1 and melanoma.