MMP9 and glioma: A range of anti-inflammatory and pro-tumoral factors secreted by GAMs have been identified as playing important roles in glioma cell invasion, including transforming growth factor beta (TGF-β), epidermal growth factor (EGF), IL-6, IL-1β, stress-inducible protein-1 (STI-1), matrix metallopeptidase-2 (MMP-2), and MMP-9 (27).