Laetsch TW, et al. - The safety of larotrectinib, a highly selective small-molecule inhibitor of the TRK kinases that has shown activity in preclinical models and in adults with tumours harbouring TRK fusions, was assessed in paediatric patients included in this study conducted at eight sites in the USA. Larotrectinib was administered orally, twice daily, on a continuous 28-day schedule, in increasing doses adjusted for age and bodyweight in patients aged 1 month to 21 years with locally advanced or metastatic solid tumours or CNS tumours that had relapsed, progressed, or were non-responsive to available therapies regardless of TRK fusion status. With good tolerability in paediatric patients, larotrectinib demonstrated encouraging antitumour activity in all patients with TRK fusion-positive tumours. Regardless of age, 100mg/m² (maximum 100 mg per dose) was defined as the recommended phase 2 dose for infants, children, and adolescents.