SDF-1 and CXCR4 play a role not only in the epithelial-to-mesenchymal transition (EMT) and in the generation and self-renewal of cancer stem cells, but also in generating and maintaining the perivascular stem cell niche, regulating the migration of GSC along the pre-existing vasculature and in inducing chemo- and radio-resistance [45,46]. The gene discussed is CXCR4; the disease is cancer.