GDNF and neoplasm: Indeed, inflammatory processes and/or hypoxic microenvironment within the tumor or neighboring normal tissues likely result in secretion by GBM cells of immunomodulatory cytokines and other factors such as CSF1 (colony-stimulating factor 1), C-C/CXC motif chemokines, or GDNF (glial cell-derived neurotrophic factor), which polarize TAMs toward an immunosuppressive M2 phenotype (Chang et al., 2016; Chen et al., 2017; Wang et al., 2019).