A Case of Inv(1)(q23q31) TPR-NTRK1 Fusion-Positive Spindle Cell Neoplasm in an Infant—Uncovered by Next-Generation Sequencing: Diagnostic Challenge, Review, and Therapeutic Implications

Lately, NTRK-positive mesenchymal tumors are being increasingly identified, mostly in pediatric patients, in view of associated treatment implications, especially in recurrent and unresectable tumors. A 1-year-old male child presented with a rapidly growing tumor mass in his cervical region of 2 months duration. Radiologic imaging disclosed a tumor measuring 11 cm in size, almost filing his right neck spaces. Review of biopsy sections revealed a cellular tumor comprising spindle cells arranged in sheets and fascicles with interspersed collagenous strands and areas of adipocytic, myxoid, and hyaline degeneration. Immunohistochemically, tumor cells were diffusely positive for CD34 and S100 protein. Subsequently, on testing the tumor for a solid tumor gene panel by next-generation sequencing, it was found to be positive for inv(1)(q23q31) TPR-NTRK1 fusion. Furthermore, tumor cells displayed NTRK1 gene rearrangement by fluorescence in situ hybridization technique. The patient was offered chemotherapy; however, he had a rapid local progression, leading to respiratory obstruction; he then succumbed to the disease. The present case underpins the value of next-generation sequencing as a useful technique for uncovering NTRK-fusion–positive mesenchymal tumors. Review of similar cases, diagnostic challenge, and treatment implications in such cases are discussed.