Tissue-Agnostic Targeting of Neurotrophic Tyrosine Receptor Kinase Fusions: Current Approvals and Future Directions

NTRK fusions are oncogenic drivers for multiple tumor types. Therefore, the development of selective tropomyosin receptor kinase (TRK) inhibitors, including larotrectinib and entrectinib, has been transformative in the context of clinical management, given the high rates of responses to these drugs, including intracranial responses in patients with brain metastases. Given their promising activity in pan-cancer cohorts, larotrectinib and entrectinib received U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA) approval for tissue-agnostic indications in patients with advanced solid tumors harboring NTRK fusions. The safety profiles for both drugs are quite manageable, although neurotoxicity driven by the on-target inhibition of normal NTRK can be a concern. Also, on- and off-target resistance mechanisms can arise during therapy with TRK inhibitors, but they can be addressed with the use of combination therapy and next-generation TRK inhibitors. More recently, the FDA approved the use of repotrectinib, a second-generation TRK inhibitor, in patients with NTRK fusions, based on data suggesting clinical efficacy and safety, which could offer another tool for the treatment of NTRK-altered cancers. In this review, we summarize the current evidence related to the use of TRK inhibitors in the tissue-agnostic setting. We also elaborate on the safety profiles and resistance mechanisms from a practical perspective.