These astrocytes are indirectly involved in glioma spreading, including a metabolic way, by synthetizing multiple cytokines: brain-derived neurotrophic factor (BDNF), transforming growth factor α (TGF-α), sphingosine-1-phosphate, glial cell line-derived neurotrophic factor (GDNF) [7, 27–29]. Here, GDNF is linked to central nervous system cancer.