Interestingly, the most important signalling factors found to repress tumour progression and aggressiveness include MSC-related paracrine-soluble secreted factors and MSCs-derived molecules released from exosomes; these include proven anti-proliferative factors such as Dickkopf-related protein 1 (Dkk-1), a soluble Wnt antagonist, phosphatidylinositol 3,4,5-trisphosphate 3-phosphatase (PTEN), and bone morphogenetic protein (BMP), as well as cytotoxic agents such as TNF-related apoptosis-inducing ligand (TRAIL) and TNF-α. The gene discussed is DKK1; the disease is neoplasm.