VHL and nonpapillary renal cell carcinoma: A VHL mutation stabilizes HIF-1/2-α and induces the expression of several angiogenesis-related factors [e.g., vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), and transforming growth factor-β (TGF-β)], all of which play important roles in tumorigenesis of ccRCC [15,16,17].