EGF and neoplasm: Microglia and macrophages secrete multiple cytokines, growth factors, enzymes, and reactive oxygen species that can directly or indirectly lead to angiogenesis (e.g., vascular endothelial growth factor (VEGF), tumor proliferation (e.g., EGF), and invasion (e.g., metalloproteases) of metastatic cancer cells in the brain [32].