Tropomyosin-related kinase(TRK)fusion proteins are oncogenic drivers in multiple tumors in adults and children.Larotrectinib, an orally administered selective TRK inhibitor approved in the US, exhibits inhibitory activity against tumors harboring TRK fusions and is well tolerated.Here, we report the case of an 8-year-old female child with recurrence of an NTRK fusion low-grade sarcoma treated with larotrectinib monotherapy.The patient previously underwent resection of low-grade sarcoma in the right brachialis at 6 years of age, but local recurrence occurred after 16 months.As re-operation likely required amputation, larotrectinib was commenced at a dose of 100 mg BID.Complete radiographic remission was achieved after 3 months.There were no adverse events attributed to larotrectinib treatment.After dosing for 6 months, we performed local resection, confirming pathological complete remission.The drug was stopped, and the patient showed no evidence of relapse at 4 months after resection.In this case, larotrectinib was obtained using Single Patient Expanded Access under the FDA.In this paper, we also discuss the issues faced while accessing unapproved drugs in the precision medicine era in Japan.