A80-4-12 Unusual Presentation of Inflammatory Myofibroblastic Tumor With Etv6-ntrk3 Fusion and Distant Metastasis

Abstract Introduction Inflammatory myofibroblastic tumor (IMT) is a rare mesenchymal neoplasm, accounting for approximately 20 percent of all primary lung tumors in children aged 9-10 years. About 50 percent of IMTs contain ALK gene translocation, while NTRK fusions are much less common. Rarely it presents with distant metastasis. We present a case of IMT with ETV6-NTRK3 fusion and distant metastases. Case Report Patient is 25-year-old male presented to hospital after sustaining a rib fracture during minor trauma. Initial CT chest revealed 3 x 5 cm lung mass. Repeat PET/CT after a year showed a significantly increased size of the mass up to 14 x 9.7 x 13.7 cm mass involving the right lung with FDG avidity (Figure1). Biopsy confirmed inflammatory myofibroblastic tumor, and molecular testing identified an ETV6-NTRK3 fusion. The patient underwent resection of lung mass with partial pleurectomy. He was started on larotrectinib and denosumab. denosumab was discontinued due to intolerance, and entrectinib was initiated. Despite these targeted therapies, the disease progressed. Imaging revealed osseous metastases in the thoracic and lumbar vertebrae, multiple hepatic lesions, and metastasis to the right iliac wing. Given continued progression, the patient was started on AIM (adriamycin, ifosfamide, mesna) chemotherapy. After two cycles, PET/CT showed new and increased hepatic, soft tissue, and bone metastases. Palliative care was consulted for symptom management. Discussion IMT is generally indolent, with rare metastatic potential. Treatment for localized IMT is surgical resection; advanced/unresectable or metastatic IMT are mostly resistant to chemotherapy. Targeted therapies, such as larotrectinib, entrectinib, or repotrectinib, are first-line options for NTRK fusion-positive tumors. This case highlights a rare, aggressive IMT subtype with ETV6-NTRK3 fusion and distant metastases, demonstrating resistance to both NTRK inhibitors and cytotoxic chemotherapy. Conclusion Inflammatory myofibroblastic tumor with ETV6-NTRK3 fusion is a rare sarcoma subtype. While distant metastasis is uncommon, such cases are often resistant to available therapies, including targeted agents and chemotherapy. This abstract is funded by: None