In particular, downregulation of CXCR-4 using siRNA as well as its pharmacological inhibition by AMD3100 (Plerixafor) contributed to sphere formation blockade of CXCR-4+ RCC CSCs, and increased their responsiveness towards anti-angiogenic agents Sunitinib, Sorafenib and Pazopanib [56]. This evidence concerns the gene CXCR4 and renal cell carcinoma.