An angiogenic growth factor produced by tumor cells, it is able to induce specific malignant characteristics in normal cells (such as fibroblasts), thereby “transforming” those cells. TGF-beta stimulates blood vessel growth, even though it inhibits the division of endothelial cells. TGF-beta is a strong “attracting agenf for macrophages (i.e., TGF-beta is chemotactic), and appears to be responsible for the high concentrations of macrophages that are often found in tumors. TGF-beta has shown immunosuppressive activity (i.e., it suppresses the immune system).