CCL2 and neoplasm: The tumor microenvironment is a site where chemokines and cytokines, such as VEGF, urokinase plasminogen activator (uPA), IL-8, transforming growth factor beta-1 (TGF-b1), and monocyte chemotactic protein-1, are abundantly secreted, and these molecules may induce the homing of MSCs [13, 31].