Bevacizumab is an experimental drug that blocks a molecule called VEGF that is found in high amounts in malignant gliomas. VEGF promotes the growth of blood vessels that bring nutrients to tumor cells. In studies with laboratory animals, Bevacizumab slowed the growth of several different types of human cancer cells by blocking the effects of VEGF. There is also evidence that Bevacizumab enhances the effects of radiation on tumor cell