VEGFA and neoplasm: The immature vessels formed during this process are fenestrated and lack endothelial tight junction protein complexes allowing increased vascular permeability.16 These immature capillaries are “leaky” compared to normal BBB capillaries.17 While the lesion continues to grow in size, the tumor becomes more hypoxic and secretes vascular endothelial growth factor (VEGF) to induce more angiogenesis.18 This dynamic process contributes to BTB permeability.