In addition to the SDF-1/CXCR4 axis, multiple other molecules have been found to mediate the tumor tropism of MSCs, such as hepatocyte growth factor (HGF) [51], monocyte chemoattractant protein 1 (MCP-1) [52], tumor growth factor β (TGF-β) [53], hypoxia-inducible factor (HIF) [54], and platelet-derived growth factor (PDGF) [55]. The gene discussed is CXCR4; the disease is neoplasm.