A naturally-occurring form of vitamin E, a fat-soluble vitamin with potent antioxidant properties. Considered essential for the stabilization of biological membranes (especially those with high amounts of polyunsaturated fatty acids), d-alpha-Tocopherol is a potent peroxyl radical scavenger and inhibits noncompetitively cyclooxygenase activity in many tissues, resulting in a decrease in prostaglandin production. Vitamin E also inhibits angiogenesis and tumor dormancy through suppressing vascular endothelial growth factor (VEGF) gene transcription. Check for active clinical trials using this agent. (NCI Thesaurus)