GDNF and central nervous system cancer: This reciprocal activation has not been highlighted for GDNF (glial-derived neurotrophic factor) that does not exert paracrine effect to induce astrogliosis (Ku et al., 2013), but when released by astrocytes enhances the growth and invasion of the tumor (Shabtay-Orbach et al., 2015), and when released by the tumor acts autocrinally to strengthen glioma growth (Lu et al., 2010).