CXCR4 and cancer: Hence, our data suggest a relevant influence of CXCR4 on proliferation anddifferentiation of renal cell carcinoma with regard to the in vivo situation.This hypothesis is strengthened by observations in a murine model, where themetastatic capability of CXCR4-expressingRCC cells strongly correlated with CXCR4 protein level on cancer cells and the SDF-1α expression in the target organs [23].