NGF and neoplasm: Neurotrophins, as nerve growth factor (NGF), when released by macrophages, mast cells, and other leukocytes could be promoting to axonogenic switch for tumor innervation, as occurs in inflammatory pain178 and neurogenesis by recruiting brain-derived neural precursors for cancer progression (Section “Tumor neurogenesis: CNS-derived neural progenitor cells infiltrated in tumors”).