TRK Inhibition: A New Tumor-Agnostic Treatment Strategy.

Oncogenic somatic chromosomal rearrangements involving the NTRK1, NTRK2 or NTRK3 genes (NTRK gene fusions) occur in up to 1% of all solid tumors, and have been reported across a wide range of tumor types. The fusion proteins encoded by such rearranged sequences have constitutively activated TRK tyrosine kinase domains, providing novel therapeutic anticancer targets. The potential clinical effectiveness of TRK inhibition in patients with tumors harboring NTRK gene fusions is being assessed in phase I and II trials of TRK inhibitors, such as larotrectinib and entrectinib. Clinical trial results have demonstrated that larotrectinib is generally well tolerated and has shown high response rates that are durable across tumor types. These data validate NTRK gene fusions as actionable genomic alterations. In this review, we present the clinical data, discuss the different approaches that might be used to routinely screen tumors to indicate the presence of NTRK gene fusions, explore the issue of acquired resistance to TRK inhibition, and reflect on the wider regulatory considerations for tumor site agnostic TRK inhibitor drug development.