Thrombospondin-1 is believed to play a role in cell migration and proliferation, during embryogenesis and wound repair. It has also been used as a potential regulator of tumor growth and metastasis. TSP expression is highly regulated by different hormones and cytokines and is developmentally controlled. TSP stimulates the growth of vascular smooth muscle cells and human foreskin fibroblasts. A combination of IFN-gamma and TNF-alpha inhibits TSP production in these cells.