Intracranial mesenchymal tumor with FET::CREB fusion: a rare case report.

Purpose: This case report aims to enhance awareness and understanding of intracranial mesenchymal tumors with FET::CREB fusion by illustrating the associated diagnostic challenges, thereby contributing to the limited literature on this rare entity. Methods: This report presents a case of a 58-year-old female who presented with a persistent headache. Neuroimaging revealed a well-defined cystic mass in the right temporoparietal lobe. The patient underwent gross total resection (GTR). Results: Histopathological analysis was consistent with an intracranial mesenchymal tumor, showing immunopositivity for Desmin, MUC4, CD99, and ALK. Next-generation sequencing identified an EWSR1::ATF1 gene fusion, confirming the diagnosis of an intracranial mesenchymal tumor, FET::CREB fusion-positive. Approximately two years postoperatively, follow-up imaging revealed local tumor recurrence, which was managed with a second GTR. Conclusion: This case highlights the diagnostic challenges, potential for recurrence, and importance of molecular profiling in the accurate diagnosis of this rare tumor entity. GTR remains the primary treatment, though the long-term biological behavior and optimal management strategies require further investigation.