SDF-1α/CXCL12, which has been demonstrated to affect cancer cell proliferation [63, 64] and metastasis [15], must directly affect MDA-MB-231 behavior, probably through the SDF-1α/CXCL12 receptor, which has been shown to be expressed in MDA-MB-231 cells [65]. The gene discussed is CXCL12; the disease is cancer.