CXCL12 and neoplasm: As we have recently reviewed [22], mounting evidence now suggests that MSCs possess leukocyte-like, active homing mechanisms for tumor tropism involving a variety of adhesion molecules (e.g., P-selectin and vascular cell adhesion molecule-1) and tumor-derived cytokines, chemokines, and growth factors (e.g., CXCL12 and platelet-derived growth factor).