Huge primary mediastinal synovial sarcoma fully occupying the right hemithorax

Primary mediastinal synovial sarcomas are exceedingly uncommon tumors. Herein, we present the case of primary mediastinal synovial sarcoma (monophasic spindle cell-shaped variant) fully occupying the right hemithorax in a 37-year-old woman who presented to clinic with a 2-month history of right-sided chest pain and shortness of breath. Although extremely rare, however, synovial sarcoma should be considered in the differential diagnosis of all monophasic and biphasic spindle cell neoplasms of the mediastinum. Despite molecular testing for (t[x; 18] [p11.2; q11.2]) is characteristically positive in 90% of synovial sarcoma cases, it is not routinely done. Histopathological and immunohistochemical analyses can greatly confirm the diagnosis. Optimal surgical resection is the standard of care. Adjuvant therapy (radiotherapy and/or chemotherapy) is indicated in inoperable advanced disease or unachieved surgical tumor-free surgical margins. Prognosis is poor with a 5-year overall survival (OS) rate of 35.7%. Early diagnosis and prompt appropriate management yield better disease-free and OS rates.