primary pulmonary synovial sarcomas are extremely rare neoplasms with an unknown cause originating from mesenchymal tissue and accounting for 10% of soft tissue sarcomas . although most synovial sarcoma tumors are located in soft tissue , especially near large joints of the extremities , they also can occur in numerous situations unrelated to joint structures . thoracic involvement of the synovial sarcoma is rare , and only a few cases have been reported in the literature . we report the case of a 69-year - old asymptomatic man , a heavy smoker with no clinically relevant family or personal history . the patient was admitted to our institution for study of a solitary pulmonary nodule found after routine chest x - ray , not present in previous examinations . computed tomography ( ct ) scan showed a 23 mm multilobulated nodule in the right upper lobe with peripheral calcification ( fig . the standardized uptake value of the pulmonary nodule in positron emission tomography - computed tomography ( pet - ct ) scan was 1.5 g / ml . bronchoscopy did not reveal any endobronchial lesion . a ) chest ct scan shows a multilobulated nodule in the right upper lobe with peripheral calcification . b ) spindle cell proliferation organized in irregular fascicles , without epithelial component in tumor cells ( h / e 40 ) . c ) intense immunohistochemical expression of cd99 membrane marker in tumor cells ( 40 ) in order to resect the nodule , a video - assisted thoracoscopic surgery ( vats ) right upper lobectomy with systematic lymph node dissection was performed . pathological examination revealed a well - defined tumor , not encapsulated , with spindle cells ( fig . immunohistochemically , neoplastic cells were positive for vimentin , cd56 and bcl-2 , and focally positive for cd99 ( fig histologically , primary pulmonary synovial sarcoma can be classified into four categories : biphasic , monophasic fibrous ( spindle cells ) , monophasic epithelial and poorly differentiated types . macroscopically , these tumors are well circumscribed and not encapsulated , with a very variable size ranging from 0.6 to 27 cm ( mean : 6.8 ) synovial sarcomas are positive for cytokeratin 7 and 19 , ema , bcl-2 , cd99 and vimentin . they are usually negative for s-100 , cd-34 , desmin , actin and vascular tumor markers [ 35 ] . recent cytogenetic studies have taken a leading role for definitive diagnosis of synovial sarcoma , identifying a translocation t(x;18 ) ( p11.2;q11.2 ) resulting from fusion of the syt gene on chromosome 18 to ssx1 or ssx2 on chromosome x . differential diagnosis includes other malignant extrathoracic tumors such as fibrosarcomas , carcinosarcomas , leiomyosarcomas or hemangiopericytomas . the prognosis for patients with primary pulmonary synovial sarcoma is poor , with an overall 5-year survival rate of 50% . negative prognostic factors are tumor size , male gender , extensive tumor necrosis , higher histological grade , mitotic rate and neurovascular invasion . the expression of syt - ssx1 variants has been associated with worse behavior .
primary pulmonary synovial sarcoma is an extremely rare tumor with an unknown cause . 
 the diagnosis is established after other primary lung malignancies or metastatic extrathoracic sarcoma have been excluded . 
 we report the case of a 69-year - old man who presented with a well - defined mass in the right upper lobe on a chest x - ray . a video - assisted thoracoscopic surgery ( vats ) 
 right upper lobectomy was performed . 
 immunohistochemically , neoplastic cells were positive for vimentin , cd56 and bcl-2 , and focally positive for cd99 , epithelial membrane antigen and cytokeratin 7 and 19 . 
 the cytogenetic study revealed a syt genetic reassortment . 
 so , the final pathological diagnosis was primary pulmonary synovial sarcoma .