DKK1 and neoplasm: MSCs can block Wnt signaling by regulating the Dickkopf-related protein 1 (DKK1) secreted by tumor cells, downregulating c-Myc and Cyclin D2 and upregulating the expression of P21CIP1 and P27KIP1, resulting to tumor cell suppression (Qiao et al., 2008; Zhu et al., 2009).