NGF and neoplasm: Moreover, bidirectional communication between neurons and cancer cells accelerates tumor development and progression.295–297 Specifically, cancer cells induce the outgrowth of nerves in the tumor microenvironment through paracrine-acting neurotrophic factors (e.g., NGF, BDNF) and axon guidance molecules, and in turn, nerves release neurotransmitters in the tumor microenvironment that stimulate cancer cell proliferation, invasion, and metastasis.