BDNF and neoplasm: In this process, known as neoaxonogenesis, cancer and other cells in the tumor microenvironment play an important role by synthesizing and releasing neurotrophic factors (e.g., nerve growth factor, brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor), axonal guidance molecules (netrins, semaphorins, ephrins, slits), exosomes (containing microRNA and axonal guidance molecules), and other molecules present in the tumor microenvironment (e.g., granulocyte colony-stimulating factor, leukemia inhibitory factor), which modulate the ingrowth of nerve fibers into the tumor.