clear - cell sarcoma ( ccs ) is a rare malignant connective tissue tumor that was first described by enzinger in 1965 .
ccs occurs most commonly in adolescents and young adults and the patients aged > 60 years are rare .
it has a high rate of local recurrence , regional lymph node metastasis , and distant metastasis [ 1 , 2 ] .
ccs occurs most commonly in the deep soft tissues of the extremities , with rare involvement of the head , neck , and trunk .
we experienced a very rare case of primary ccs in the mediastinum with successful surgical resection in an elderly patient .
in october 2011 , a 63-year - old man presented with a mass in the right upper mediastinum on chest radiograph .
computed tomography showed a large oval mass ( 55  55  85 mm ) with clear margins and heterogeneous enhancement in the right upper posterior mediastinum between the phrenic nerve and vertebrae ( fig .
1b ) , and 18f - fluorodeoxyglucose positron emission tomography showed abnormal uptake with a maximum standardized uptake value of 15.1 .
the tumor was excised by video - assisted thoracoscopic surgery , with negative surgical margins .
the tumor was soft , well circumscribed , encapsulated , and did not invade the pleura .
histological examination of the resected tumor with hematoxylin and eosin ( he ) staining showed morphological features compatible with conventional soft tissue ccs .
the tumor cells were distributed in nests separated by fibrous connective tissue , showing an alveolar pattern ( fig .
the tumor cells had eosinophilic and clear cytoplasm and oval vesicular nuclei of varying sizes with characteristic prominent eosinophilic nucleoli .
2c ) , s-100 protein , calretinin , cd34 , cd56 , cd68 , and cd117 ; and negative for melan - a , cytokeratins ae1ae3 , cytokeratin cam5.2 , chromogranin a , desmin , caldesmon , myogenin , epithelial membrane antigens , cd57 , cd99 , and d2 - 40 .
ccs is a very rare soft tissue neoplasm , which occurs in the extremities in 9095% of cases .
our case was diagnosed with a primary ccs in the mediastinum . a search of the english literature revealed only one previously reported case of primary ccs in the mediastinum .
recent cytogenetic studies showed that ccs is associated with the translocation t(12;22 ) ( q13;q12 ) ; this translocation is observed in up to 93% of patients with ccs , but never observed in malignant melanoma . in our case
, we were unable to determine whether this translocation was present , because of the lack of availability of such analysis in japan .
the rarity of ccs in the mediastinum makes it difficult to draw conclusions regarding prognostic factors .
reported that complete excision of the primary tumor with wide surgical margins appears to be the optimal approach to treatment , with or without adjuvant radiation therapy .
ccs is an aggressive malignant tumor , and unlike most soft tissue sarcomas , it often metastasizes to regional lymph nodes . in our case
, we did not have a definitive diagnosis at the time of operation , and therefore we did not perform excision of the tumor with wide margins or dissect the regional lymph nodes . in most cases , ccs has a relentlessly progressive course and results in death because of widespread dissemination .
the reported overall survival rates without local recurrence are 30% at 5 years and 16% at 10 years .
some patients experience rapidly fatal progression , and late metastasis after many years of freedom from disease is also relatively common .
we believe that regular long - term follow - up with computed tomography , magnetic resonance imaging , and 18f - fluorodeoxyglucose positron emission tomography examination is important to identify local recurrence or distant metastasis as early as possible .
 we report a case of primary clear - cell sarcoma ( ccs ) in the mediastinum . in october 2011 
 , a 63-year - old man was admitted to our hospital for surgical resection . 
 the tumor was completely excised by video - assisted thoracoscopic surgery . 
 the tumor was well encapsulated and did not invade the pleura . 
 histological examination led to a final diagnosis of primary ccs in the mediastinum . 
 the patient remains alive without evidence of recurrence at 15 months after surgery . 