The chemokine CXCL12 (stromal cell-derived factor-1 (SDF-1)) binds primarily to CXC receptor 4 (CXCR4), establishing CXCL12–CXCR4 signaling pathway and are involved in the cross-talk between cancer cells, stromal cells, T cells, and their microenvironment, including the regulation and direction of T cell migration (chemotaxis), proliferation, and differentiation of immature progenitor-stem cells [2]. The gene discussed is CXCL12; the disease is cancer.