STAT3 and neoplasm: In addition, there may be a positive feedback mechanism during malignant cell transformation between STAT3 and VEGF, namely, STAT3 upregulates VEGF, while VEGF combines with the cellular surface VEGF receptor (VEGFR) to activate the IL-6/STAT3 signaling pathway to further upregulate expression of VEGF and promote the generation of blood vessels in tumor tissues.