Spinal EWSR1::CREM fused mesenchymal tumor: an extracranial CNS counterpart of intracranial mesenchymal tumor, FET::CREB‑fusion positive.

The occurrence of mesenchymal tumor, FET::CREB fusion-positive in the spinal compartment is exceptionally rare, with only a few previously documented cases. Here, we present a unique case of a 43-year-old man who developed a mesenchymal tumor, FET::CREB fusion-positive at the T1 spinal level. Clinically, the patient reported chronic posterior neck and shoulder pain accompanied by the intermittent paresthesia of the right arm. Magnetic resonance imaging demonstrated an intradural extramedullary mass, initially suggestive of a schwannoma. The patient underwent near-total surgical removal via a right C7-T1 hemilaminectomy. Histological examination revealed epithelioid and cord-like cellular arrangements within a mixed sclerotic and myxochondroid stroma. Immunohistochemistry revealed partial positivity for epithelial membrane antigen (EMA), smooth muscle actin (SMA), and CD99. Molecular analysis confirmed the presence of EWSR1::CREM fusion, establishing the diagnosis of a mesenchymal tumor, FET::CREB fusion-positive. To date, all reported spinal mesenchymal tumors within this molecular category have exclusively featured CREM as an FET gene family fusion partner, thereby highlighting a potential site-specific molecular signature. In this case report, we discuss the potential diagnostic challenges, characteristic pathological spectra, and clinical considerations associated with this rare entity of the spine.