Abstract

Thrombospondin (TSP‐1) is a large glycoprotein secreted by platelets and synthesized by many cell types, including endothelial and tumor cells. Although controversy exists about the biological function of TSP‐1, the following observations suggest that TSP‐1 may potentiate tumor progression. (1) Tumor metastases in mice are promoted by TSP‐1 and inhibited by anti‐TSP‐1 antibodies. (2) TSP‐1 promotes tumor cell adhesion, migration and invasion. (3) TSP‐1 promotes angiogenesis in the rat aorta model. (4) TSP‐1 up‐regulates the plasminogen activator system through a mechanism involving the activation of TGF‐β1. (5) Human tumors express increased levels of the CSVTCG‐specific TSP‐1 receptor. (6) Tumor stroma is enriched in TSP‐1. (7) Cancer patients have high blood levels of TSP‐1. (8) Poor patient survival correlates with a higher expression of the CSVTCG‐specific TSP‐1 receptor on tumor cells. In this paper we discuss the evidence that TSP‐1 promotes tumor progression and present a hypothetical scheme for its mechanism of action.