A case of intracranial myxoid mesenchymal tumor with EWSR1:CREM fusion in an adult female: Extensive immunohistochemical evaluation.

Intracranial myxoid mesenchymal tumor (IMMT) is a recently described, extremely rare group of neoplasms characterized by fusions between the female-expressed transcript (FET) family genes and the cAMP response element-binding protein (CREB) family genes. Controversy persists regarding whether the tumor is a myxoid variant of angiomatoid fibrous histiocytoma or a completely distinct clinicopathological entity. Here, we report a case of IMMT arising in the posterior fossa in a 65-year-old woman with a history of breast cancer. We performed total removal of the tumor, which histologically demonstrated features characteristic of IMMT but also bore a partial resemblance to conventional angiomatoid fibrous histiocytoma. Immunohistochemically, tumor cells were diffusely positive for desmin, vimentin, cluster of differentiation (CD) 99 (CD99), glucose transporter-1, and cytokeratin (CK) 8/18 (CK8/18), and focally positive for CK7, epithelial membrane antigen, mucin 4, anaplastic lymphoma kinase, calponin, and CD68. Molecular genetic analysis revealed a fusion between the Ewing sarcoma breakpoint region 1 (EWSR1) gene (EWSR1) and the cAMP-responsive element modulator (CREM) gene (CREM) called EWSR1:CREM fusion, which confirmed the diagnosis. The overlap of the pathological features of IMMTs and angiomatoid fibrous histiocytomas may support the recent theory that these tumors are two manifestations of a single entity. Moreover, our study indicated the broad spectrum of immunohistochemical phenotypes of these tumors, which should be noted during diagnosis. Further studies are needed to elucidate the histopathological concept, long-term prognosis, optimal treatment strategy, and factors associated with the prognosis and therapeutic options of this condition.

A non-NF2 case of schwannomas of vestibular and trigeminal nerves with different genetic alterations of NF2 gene: case report.

BACKGROUND: We report a patient with 2 separate schwannomas, a vestibular schwannoma and a trigeminal schwannoma, that were attached to each other and appeared to be a single tumor on imaging studies. CASE DESCRIPTION: The patient, without any family history of neurofibromatosis, presented with a progressive hearing loss and mild left facial nerve palsy. Magnetic resonance imaging showed a snowman-like tumor in the left cerebellopontine angle. Surgical exposure revealed that the tumor consisted of 2 "kissing" schwannomas, a trigeminal and vestibular schwannoma. Molecular genetic analysis detected a 1-base pair deletion at exon 10 of the neurofibromatosis type 2 (NF2) gene in the trigeminal schwannoma, but not in the acoustic schwannoma. However, loss of heterozygosity at chromosome 22q (D22S282 and D22S929) was detected in both tumors, losing the same allele. CONCLUSION: Multiple schwannomas in non-NF2 patients are extremely rare, and possible causes include simple coincidence or germline genetic alteration of adjacent gene on chromosome 22q, similar to the cause recently suggested in familial schwannomatosis. Although not always possible, molecular genetic examination may help to understand the underlying mechanism and would be warranted in such cases.