STAT3 phosphorylation has been shown to affect HIF-2α levels in 786-O cells and HIF-1α and HIF-2α in Caki-1 renal cancer cells [11, 47], and STAT3 phosphorylation at Tyr705 and Ser727 residues is increased in ccRCC tumors [13]. This evidence concerns the gene EPAS1 and nonpapillary renal cell carcinoma.