It is known that the excessive activation of STAT3 in tumor cells is associated with poor prognosis, and IL-6, a classic STAT3-activator produced by mesenchymal stem cells, induces STAT3 activation in tumor cells such as Saos-2 osteosarcoma cells and consequently promotes tumor proliferation and metastasis (Tu et al., 2012). The gene discussed is STAT3; the disease is osteosarcoma.