CXCR4 and neoplasm: Suppression of tumor growth is most likely achieved by the induction of MKP-1 which leads to the down-regulation of p38MAPK and ERK1/2, a PPARγ-independent event; retardation of metastases is via a PPARγ-dependent pathway which directly decreases CXCR4 and MMP expressions (Figure 6).