CD274 and cancer: Other important outstanding challenges include: (1) whether structurally modified flavonoids are equally effective in regulation of PD-L1 expression, (2) whether cancer cell types display similar or different sensitivity to modulation of PD-L1 by flavonoids, (3) nature of signaling pathways governing the control of PD-L1 by flavonoids, (4) the role of epigenetic control, specifically, histone acetylation/deacetylation, methylation/demethylation, in fine tuning the control of PD-L1 expression in response to flavonoids.