The rapid proliferation of tumor cells leads to tumor ischemia and hypoxia, which directly stimulates angiogenesis and promotes the secretion of cytokines such as matrix metalloproteinase-9 (MMP9), C-X-C motif chemokine ligand 12 (CXCL12) and Wnt7B by various cells, especially tumor cells. The gene discussed is CXCL12; the disease is neoplasm.