Thrombospondin-1 (TSP-1) is a member of a family of five structurally related extracellular glycoproteins that plays a major role in cell-matrix and cell-cell interactions. Due to its multifunctional nature and its ability to bind to a variety of cell surface receptors and matrix proteins, TSP-1 has been identified as a potential regulator of angiogenesis and tumor progression. In this review, we summarize recent results that we obtained in our laboratory dealing with the regulation of thombospondin-1 expression by epidermal growth factor and hepatocyte growth factor. Our results show that TSP-1 can have opposite effects on cell invasion depending upon the type of differentiated thyroid carcinoma studied.