Clinicopathological and Genomic Features of Pediatric Intracranial Myxoid Mesenchymal Tumor with both of Gene Fusion and Mutation: A Case Report and Comparison with Adult Cases in the Literature.

Intracranial myxoid mesenchymal tumors (IMMTs) with family gene fusion are rare brain neoplasms characterized by gene fusion between the gene and one of the cyclic AMP response element-binding (CREB) family transcription factor (, , or ) genes. Although half of reported cases are pediatric, the clinical, histologic, and genomic features of IMMTs with rearrangement in pediatric populations are not yet well clarified. Here we describe the case of a 7-year-old girl who presented with seizures due to an extra-axial tumor in the left parietal convexity. Gross total resection was achieved, and the tumor displayed a multilobular structure with solid hypercellular and myxoid hypocellular areas, separated by a variable amount of stroma. The hypercellular areas consisted of round to polygonal cells, whereas the myxoid areas were ovoid to spindled cells. Immunophenotypically, the tumor cells were positive for vimentin, desmin, and EMA. Next-generation sequencing of tumoral DNA revealed gene fusion and a pathogenic mutation of . No recurrence was detected 9 months after resection, without chemotherapy or radiotherapy. In comparison to other pediatric and adult patients with rearrangement, many clinical, radiological, and immunohistochemical features were shared. However, signs of elevated intracranial pressure were more frequently observed, and postoperative radiation was less frequently administered for pediatric patients. Gross total resection (GTR) was the key prognostic factor for better disease control especially among pediatric patients. Further reports of cases with rearrangement with detailed genetic profiles are essential for clarifying the oncogenic pathway and establishing a standard treatment strategy.