In addition, several authors have evaluated the levels of plasma neuropeptide Y (NPY), brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), placental growth factor (PlGF), S100B, interleukin 8 (IL-8) and glial fibrillary acidic protein (GFAP) in patients with different types of CNS tumors [21]. Here, GDNF is linked to central nervous system neoplasm.