[Intracranial mesenchymal tumors with FET::CREB fusion: a clinicopathological analysis of six cases].

Objective: To investigate the clinicopathological and molecular genetic characteristics of intracranial mesenchymal tumors with FET::CREB fusion transcript. Methods: The clinical and imaging data of 6 cases of intracranial mesenchymal tumors with FET::CREB fusion from December 2018 to December 2023 were collected at the First Affiliated Hospital of Zhengzhou University. Their histological features, immunophenotype and molecular characteristics were analyzed. Results: Among the 6 patients, 4 were males and 2 were females, and the median age was 20 years. The clinical symptoms were increased intracranial pressure in 5 cases and epilepsy in 1 case. The lesion sites were cerebellum (2 cases), frontal lobe (2 cases), parietal lobe (1 case), and cranioorbital communication (1 case). The radiological features mainly showed solid or cystic components, with obvious annular enhancement on MRI. The histopathological features showed a wide spectrum of morphology, clear boundaries and fibrous pseudocapsule. The tumor cells were arranged in a lamellar or nodular pattern, and some in cord or loose network. The tumor cells were spindle, oval, epithelioid or stellate. The stroma was collagenous or mucin-rich, and accompanied by abundant lymphocytes and plasma cells infiltration. By immunohistochemical staining, desmin, CD99 and EMA were expressed in 6 cases, CD68 in 1 case, MUC4 in 1 case, synaptophysin in 2 cases, and ALK in 1 case. The Ki-67 proliferation index was between 1%-15%. Molecular analysis showed EWSR1::ATF1 fusion in 3 cases, EWSR1::CREB1 fusion in 2 cases, and EWSR1::CREM fusion in 1 case. Conclusions: Intracranial mesenchymal tumors with FET::CREB fusion are relatively rare and typically occur in children and younger adults. These tumors have a broad morphological spectrum and often express desmin, CD99 and EMA. The molecular characteristics are the gene fusions of FET family (mainly EWSR1, FUS) with CREB family transcription factors (ATF1, CREB1 or CREM). It is necessary to distinguish these tumors from meningiomas and solitary fibrous tumors, and the combination of immunohistochemical staining and molecular genetic testing can effectively help identify these tumors.