STAT3 and neoplasm: Mechanistically, we determined that the reduction of PD-1 is related to the VEGF-A–VEGFR-2 axis which is indirectly regulated by PG attenuating the secretion of VEGF-A derived from tumor cells, and we further proved that the reduction of VEGF-A is due to the downregulation of the phosphorylation of STAT3.