• Yuta Kubota, Masanori Kawano, Tatsuya Iwasaki, Ichiro Itonaga, Hiroshi Tsumura, Nobuhiro Kaku, and Kazuhiro Tanaka.
• Department of Orthopaedic Surgery, Oita University Faculty of Medicine, Yufu City, Oita, Japan.
• Medicine (Baltimore). 2023 Dec 8; 102 (49): e36232e36232.

RationalePrecision medicine and tumor-agnostic treatment strategies have recently been promoted for clinical use. One of the most successful treatments in patients with neurotrophic tyrosine receptor kinase (NTRK) fusion-positive tumors is targeting the tropomyosin receptor kinase (TRK) with an inhibitor. The TRK inhibitors, larotrectinib, and entrectinib, have been approved in many countries. Nevertheless, the most effective administration regimen for these TRK inhibitors is uncertain. To date, no reports have shown the efficacy of sequential treatment with larotrectinib and entrectinib in patients with NTRK fusion-positive tumors. In this report, we present a patient with NTRK fusion-positive sarcoma arising from the anterior mediastinum, with tumor progression after 4 months of entrectinib use. The patient took larotrectinib subsequently and maintained disease control for more than 21 months.Patient ConcernsA 48-year-old female visited a physician because she experienced difficulty in breathing and chest and back pain with no obvious cause 2 months ago. Computed tomography (CT)-guided biopsy was performed at a district general hospital, and histopathological examination revealed a small round cell tumor. She was referred to our hospital, and a second CT-guided biopsy was performed to confirm the pathological diagnosis. Considering the results of the histopathological examination, Ewing sarcoma was suspected, but a specific fusion gene was not detected due to poor quality specimens.DiagnosesAfter 3 regimens of cytotoxic chemotherapy, biopsy was repeated, and specimens were analyzed using next-generation sequencing. The PHF20-NTRK1 fusion gene was detected, and the tumor was finally diagnosed as an NTRK fusion-positive sarcoma.InterventionsShe was administered the TRK inhibitor entrectinib, but the tumor started to grow after 4 months of medication, and she stopped taking entrectinib. After 1 cycle of cytotoxic chemotherapy, another TRK inhibitor, larotrectinib, was administered.OutcomesHer stable disease was maintained for more than 21 months. Here, we have shown that sequential administration of both drugs can be effective.LessonsIn the treatment of NTRK fusion-positive tumors, there are cases in which 2 approved first-generation TRK inhibitors can be used sequentially.Copyright © 2023 the Author(s). Published by Wolters Kluwer Health, Inc.

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