IGF1 and neoplasm: Receptor activator of nuclear factor kappa B ligand (RANKL) and other such factors secreted from tumor cells help to polarize non-transformed astrocytes, inducing them to produce pro-tumorigenic cytokines (TGF-β, IL-10, IL-6, and insulin-like growth factor 1 (IGF-1)) that enhance tumor growth and infiltration [63,64].