Tehran University of Medical Sciences (TUMS) Academic Journal of Surgery 2423-3218 3 3-4 2017 03 26 63 65 EN Reza Ershadi Assistant Professor, Department of Thoracic Surgery, School of Medicine AND Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran Mohammad Rahim Assistant Professor, Department of Thoracic Surgery, School of Medicine AND Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran Hamidreza Davari Associate Professor, Department of Thoracic Surgery, School of Medicine AND Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran 2016 07 19 2017 03 26 Background: Synovial sarcomas commonly occur in the extremities of young adults. A primary occurrence in the mediastinum is very rare with only a few reported cases in the world literature. Case Report: This paper is about a 47-year-old male who presented with retrosternal chest pain and shortness of breath on exertion. Imaging showed an anterior mediastinal mass. Pathological examination of the resected mass showed a biphasic neoplasm with a spindle cell component admixed with gland-like elements. The tumor showed positive staining with cytokeratin, epithelial membrane antigen, and vimentin confirming the diagnosis of a biphasic synovial sarcoma. Conclusions: A wide range of neoplasms, both primary and metastatic, occurs in the mediastinum, which poses considerable diagnostic difficulties. A synovial sarcoma should always be considered in the differential diagnosis, and immunohistochemistry is an important adjuvant tool in this situation. This paper highlights the importance of recognizing an unusual presentation of this aggressive neoplasm to aid appropriate clinical management. https://ajs.tums.ac.ir/index.php/ajs/article/view/64 https://ajs.tums.ac.ir/index.php/ajs/article/download/64/49