For example, the secretion of growth factors and cytokines by astrocytes can stimulate tumor cell growth, including astrocyte-derived interleukin 6 (IL-6), transforming growth factor-beta (TGFβ) and insulin-like growth factor 1 (IFG-1) which have been shown to increase tumor cell proliferation [34,35]. Here, IGF1 is linked to neoplasm.