CXCR4 and neoplasm: Since tumor cells and their microenvironments secrete chemokines or cytokines, these may be responsible for upregulating the expression of the chemokine and cytokine receptors on the hUMSCs (28,29), such as C-X-C chemokine receptor type 4 (which is upregulated in hUMSCs) and stromal cell-derived factor 1 (secreted by hUMSCs), leading to an effect on MSC migration (30,31).