Surgical Resection and Targeted Therapy in a Pediatric NTRK-Rearranged Low- Grade Spindle Cell Sarcoma: A Case Report

Background Neurotrophic tropomyosin receptor kinase (NTRK) gene fusions have emerged as important oncogenic drivers across a wide range of malignancies, including soft tissue sarcomas. Early detection of these fusions facilitates precision treatment with TRK inhibitors, significantly improving clinical outcomes. However, diagnosing NTRK-rearranged spindle cell neoplasms (NTRK-RSCNs) remains challenging due to their histological heterogeneity and overlap with other soft tissue tumors. Case Presentation We report the case of an 8-year-old boy with a history of infantile fibromatosis, who developed progressive right ankle dorsiflexion weakness and right foot drop. Magnetic resonance imaging revealed a large, homogeneously enhancing soft tissue mass with extensive perineural involvement and spinal cord compression spread from T8 to L3 levels. The patient underwent T10–L1 laminectomy and partial tumor resection under intraoperative neurophysiological monitoring. Diagnosis, Treatment and Outcome Histopathological analysis identified a low-grade spindle cell neoplasm with focal positivity for S100 and CD34, and patchy pan-tropomyosin receptor kinase (TRK) expression. Molecular studies using fluorescence in situ hybridization and RNA-based next-generation sequencing confirmed a TPM3-NTRK1 fusion, establishing the diagnosis of NTRK-rearranged low-grade spindle cell sarcoma. Postoperatively, targeted therapy with a TRK inhibitor-Larotrectinib (100 mg/m²/dose twice daily) was initiated. Over a two-year follow-up period, the patient demonstrated significant neurological improvement and stable disease without evidence of progression on serial imaging studies. Conclusion This case underscores the importance of integrating molecular diagnostics into the evaluation of atypical spindle cell tumors, particularly those presenting with aggressive clinical features despite low-grade histology. Early identification of NTRK fusions enables timely initiation of TRK inhibitor therapy, offering durable disease control and functional recovery. Broader awareness and implementation of molecular testing can greatly enhance the management of rare pediatric sarcomas.