This kind of cerebral edema is a significant cause of morbidity and mortality in patients with brain tumors and characterized by a disruption of the blood brain barrier and vasogenic edema. The exact mechanism is unclear but hypothesized that cancerous glial cells (glioma) of the brain can increase secretion of vascular endothelial growth factor (VEGF), which weakens the tight junctions of the blood–brain barrier. Historically, corticosteroids such as dexamethasone were used to reduce brain tumor-associated vascular permeability through poorly understood mechanisms and was associated with systemic side effects. Agents that target the VEGF signaling pathways, such as cediranib, have been promising in prolonging survival in "rat" models but associated with local and systemic side effects as well.