This mechanism is supported by a variety of molecules, including nerve growth factors (NGF) secreted by tumor cells and other nontumor cells in the tumor microenvironment, glial cell lineage-derived neurotrophic factors (GDNF), nerve cell adhesion molecules (NCAM), matrix metalloproteinases (MMPs) and chemokines.[19] The role of chemokines and their receptors in malignant tumors has recently received significant attention among these molecules. The gene discussed is NGF; the disease is cancer.