Tropomyosin receptor kinase B (TrkB), also known as tyrosine receptor kinase B, or BDNF/NT-3 growth factors receptor or neurotrophic tyrosine kinase, receptor, type 2 is a protein that in humans is encoded by the NTRK2 gene.
Neutrtrophic tyrosine receptor kinase (NTRK) gene fusions are implicated in various cancers, including those of lung and thyroid.
Defined as a genomic alteration in which gene rearrangements form between 3’ end of the NTRGene and the 5’ end of another gene.
This gene fusion can activate the resulting TRK protein, leading to abberant and ligand independent TRK signaling that promotes proliferation and survival signaling pathways.
TrkB is a receptor for brain-derived neurotrophic factor (BDNF).
Gene location Chromosome 9.
Tropomyosin receptor kinase B is a catalytic receptor for several “neurotrophins”, which are small protein growth factors that induce the survival and differentiation of distinct cell populations.
The neurotrophins that can activate TrkB include: BDNF (Brain Derived Neurotrophic Factor), neurotrophin-4 (NT-4), and neurotrophin-3 (NT-3).
TrkB mediates the effects of these neurotrophic factors: neuronal differentiation and survival.
Activation of the TrkB receptor can lead to down regulation of the KCC2 chloride transporter in cells of the CNS.
The TrkB receptor is part of the large family of receptor tyrosine kinases.
A tyrosine kinase is an enzyme which is capable of adding a phosphate group to certain tyrosines on target proteins, or substrates.
A receptor tyrosine kinase is a tyrosine kinase which is located at the cellular membrane, and is activated by binding of a ligand to the receptor’s extracellular domain.
There are three TrkB isoforms in the CNS.
There has been identification of NTRK1 (TrkA), NTRK2 (TrkB) and NTRK3 (TrkC) gene fusions and other oncogenic alterations in a number of tumor types.
NTRK gene fusion occur in a wide range of rare pediatric cancers.
These fusions are most frequently found in adenocarcinoma NSCLC, however, can be found in squamous cell and neuroendocrine lung cancers as well.
NSCLC tumors with oncogemic drivers such as NTRK fusions do not have a high likely response to immunotherapy.
The occurrence of NTRK fusions in an unselected pediatric population was around 2.2% of all tumors.
NTRK fusions prevalence is 0.1 to 0.3% in non-small cell lung, cancer and his highest 26% in pediatric papillary thyroid cancer.
NTRK fusion Detection methods include immunohistochemistry, fluorescence in situ hybridization, reverse transcription, polymerase chain reaction, and next generation sequencing.
NTRK fusions in non-small cell lung cancer is estimated to be between 0.1% and 0.3%.
Median age of NTRK fusion positive NSCLC is 48 years, and patients report either no or low smoking history in 73% of patients.
The prevalence of NTRK fusions IN thyroid cancer is approximately 2 to 3%.
NTRK fusion related thyroid cancer is much higher in pediatric capillary thyroid cancer.
TheTRK inhibitors larotectinib and entrectinib are recommended for patient with NTRK gene fusion positive tumors of the thyroid that are not amenable to radioactive therapy.
((Entrectinib)) a selective pan-trk receptor tyrosine kinase inhibitor (TKI) targeting gene fusions in trkA, trkB (this gene), and trkC (respectively, coded by NTRK1, NTRK2, and NTRK3 genes)
has been approved for tumors containing these abnormalities.
Larotrectinib a selective small molecule inhibitor of NTRK approved for the treatment of adult and pediatric patients with solid tumor with NTRK gene fusion.