Thrombospondin 1(TSP-1), an extracellular matrix protein, is the first identified natural angiogenesis inhibitor. A variety of normal cells, including endothelial cells, fibroblasts, adipocytes, smooth muscle cells, monocytes, macrophages, and transformed cells such as malignant glioma cells, secrete Thrombospondin 1. It regulates cellular phenotype during tissue genesis and repair. It acts as a molecular facilitator by bringing together cytokines, growth factors, matrix components, membrane receptors and extracellular proteases. Thrombospondin 1 binds to a wide variety of integrin and non-integrin cell surface receptors. It is also a major activator of transforming growth factor (TGFβ1). Secreted TSP1 is a glycoprotein with a molecular mass of 150-180 kDa.