Larotrectinib, a highly selective tropomyosin receptor kinase (TRK) inhibitor for the treatment of TRK fusion cancer.

: Detecting oncogenic drivers across multiple cancers has brought about a shift toward a more targeted therapeutic approach. Neurotrophic tyrosine receptor kinase () gene fusions are genomic rearrangements containing the kinase domain of one of three tropomyosin receptor kinases (TRK) and a dimerization domain contributed by another gene, generating fusion proteins, which are oncogenic drivers, targetable with TRK inhibitors. Larotrectinib is a first-in-class TRK inhibitor, granted accelerated FDA approval for treating TRK fusion cancer. This breakthrough indication across cancer subtypes and ages, from infancy through adulthood, highlights the need to understand the heterogeneous patient population and cancer types studied in larotrectinib clinical trials. : We provide a narrative review of preclinical, pharmacokinetic, efficacy, and safety data for larotrectinib from three clinical trials that led to regulatory approval. : Larotrectinib elicits impressive responses in most patients with TRK fusion cancer, regardless of tumor type and age. Treatment is well tolerated with a low rate of treatment-emergent grade 3-4 adverse events, dose reductions and discontinuations due to adverse events, and recent findings indicate patient-reported improvement in quality of life. This highlights the importance of early testing for gene fusions in cancers that may harbor them, even if rare.