NTRK point mutations and their functional consequences.

The neurotrophic receptor tyrosine kinase (NTRK) family of genes, including NTRK1, NTRK2, and NTRK3, encodes membrane-bound receptors that normally regulate cell survival and differentiation upon binding of growth factors. Not surprisingly, mutations in these genes are known to contribute to the growth of a diverse number of cancers. With the recent FDA approval of two first-generation tyrosine-kinase inhibitors (TKIs) for adult and pediatric patients with solid tumors harboring NTRK gene fusions, much of the literature has focused on the biology behind these types of NTRK abnormalities; however, point mutations can also contribute to oncogenesis or resistance to TKI therapy, albeit at a lower frequency than fusions. This review focuses on NTRK gene mutations that are associated with resistance to directed therapies, mutations detected in the primary setting that confer increased oncogenic activity, and evidence that suggests that some of these variants may be treated using specific targeted therapies. Finally, this review focuses on the detection of point mutations, including the utility of cell-free DNA (cfDNA) for monitoring the acquisition of resistance mutations.