These findings led to the hypothesis that CXCR4 is a biomarker that predicts the metastatic potential of RCC, and that the CXCL12/CXCR4 biological axis is regulated by VHL/HIF-1α in RCC and is a major mechanism for trafficking of RCC to metastatic sites. The gene discussed is CXCL12; the disease is renal cell carcinoma.