Myoepithelioma occurring in the posterior mediastinum harboring EWSR1 rearrangement: a case report.

Myoepithelioma is a rare neoplasm usually occurring in the salivary glands or the mammary glands but also, more rarely, in the thoracic cavity. The diagnosis of myoepithelioma is based on the presence of histological and immunohistochemical characteristics of myoepithelioma, but in unusual locations, the diagnosis is challenging. For such cases, cytogenetic approaches have been developed as helpful tools for the diagnosis. We report a surgical case of 51-year-old woman with myoepithelioma occurring in the posterior mediastinum that harbored the Ewing sarcoma breakpoint region1 (EWSR1) gene rearrangement. To the best of our knowledge, this is the first report of a myoepithelioma occurring in the posterior mediastinum. In this case, the patient underwent the thoracoscopic surgery for a diagnostic tumorectomy and was diagnosed as myoepithelioma based on the following immunohistological findings. Considering the unusual location, we additionally performed a cytogenetic analysis to confirm the presence of the EWSR1 gene rearrangement, which is a genetic characteristic of myoepithelioma.