A Case of Intracranial Mesenchymal Tumor, FET::CREB Fusion-positive, Diagnosed by Genomic Profiling with FoundationOne CDx

Intracranial mesenchymal tumor FET::cyclic adenosine monophosphate response element-binding fusion-positive is a soft tissue tumor with an extremely rare intracranial occurrence. Histological diagnosis is sometimes difficult, requiring confirmation of characteristic fusion genes. The patient was a 45-year-old male who presented with a chief complaint of pain and an abnormal sensation in the right trigeminal nerve area, in whom a neoplastic lesion in Meckel's cave was noted. The preoperative diagnoses included meningioma and schwannoma. The tumor was extirpated as much as possible, and the tumor tissue showed a high proliferative potential with rhabdoid features, raising the suspicion of a rhabdoid meningioma. However, immunostaining was positive for desmin and cluster of differentiation 99, suggesting the possibility of angiomatoid fibrous histiocytoma. For diagnosis, <i>Ewing sarcoma breakpoint region1 gene-cyclic adenosine monophosphate response element-binding 1</i> fusion and <i>Ewing sarcoma breakpoint region1 gene-activating transcription factor 1</i> fusion were examined at our institution, but were undetectable and did not lead to a diagnosis. Genomic profiling with FoundationOne CDx (Foundation Medicine, Cambridge, MA, USA) confirmed <i>Ewing sarcoma breakpoint region1 gene-cyclic adenosine monophosphate response element modulator</i> fusion and a diagnosis of intracranial mesenchymal tumor FET::cyclic adenosine monophosphate response element-binding fusion-positive was made. Diagnosis of intracranial mesenchymal tumor FET::cyclic adenosine monophosphate response element-binding fusion-positive requires both histological examination and confirmation of the fusion gene. Genomic profiling using the FoundationOne CDx is also useful when the fusion gene cannot be sufficiently confirmed at an individual's institution.