Thrombospondin-1 (THBS-1) is a member of the thrombospondin family mediating cell-to-cell and cell-to-matrix interactions. This protein can bind to fibrinogen, fibronectin, laminin, type V collagen and integrins alpha-V/beta-1. It has been shown to play roles in platelet aggregation, angiogenesis, and tumorigenesis. It is a natural inhibitor of neovascularization and tumorigenesis in healthy tissue. Both positive and negative modulation of endothelial cell adhesion, motility, and growth have been attributed to THBS-1. By blocking THBS-1 from binding to its cell surface receptor (CD47) normal tissue becomes nearly immune to cancer radiation therapy and assists in tumor death.