Tropomyosin receptor kinase B is the high affinity catalytic receptor for several "neurotrophins", which are small protein growth factors that induce the survival and differentiation of distinct cell populations. The neurotrophins that activate TrkB are: BDNF （Brain Derived Neurotrophic Factor）, neurotrophin-4 （NT-4）, and neurotrophin-3 （NT-3）. Although originally identified as an oncogenic fusion in 1982, only recently has there been a renewed interest in the Trk family as it relates to its role in human cancers because of the identification of NTRK1 （TrkA）, NTRK2 （TrkB） and NTRK3 （TrkC） gene fusions and other oncogenic alterations in a number of tumor types. A number of Trk inhibitors are in clinical trials and have shown early promise in shrinking human tumors. TrkB and its ligand BDNF have been associated to both normal brain function and in the pathology and progression of Alzheimer’s disease （AD） and other neurodegenerative disorders.