CXCR4 promotes metastasis by activating activating extracellular signal-regulated kinase 1/2 (ERK1/2), Akt/PKB and Nuclear factor-κB (NF-κB), which increases the adhesion and invasive ability of cancer cells in part by the activity of MMP2 and MMP9 [87–89]. The gene discussed is MAPK3; the disease is cancer.