although synovial sarcomas are better known to occur in the soft - tissues , these are now being increasingly recognized in the lungs as well . primary pulmonary synovial sarcomas ; however , are very rare neoplasms in the lung and pleura and have been reported to comprise less than 0.5% of pulmonary neoplasms . the poorly differentiated variant is even more rare with only isolated case reports or small series reported in literature . these are difficult to diagnose solely on the basis of the histology . in such cases , molecular techniques and the recently developed transducer - like enhancer of split 1 ( tle-1 ) antibody for use with immunohistochemistry ( ihc ) a 26-year old male presented with an increasing breathlessness over the previous 15 days accompanied by an episode of hemoptysis . on examination , he was moderately built , had low grade fever and absent breath sounds in the right lower chest . on investigation , hemoglobin and chest radiograph revealed features suggestive of a mass lesion with well - defined margins within the right lower lobe . this was followed by a high resolution computerized tomogram , which further confirmed the presence of the mass and showed it to be pulmonary and not pleural in nature . a lobectomy resection was carried out as he was determined to have no other primary site of tumor . gross examination revealed a heavy boggy right lower lobe with a congested pleural surface . on sectioning , a well - defined fleshy mass ( 13  12  5 cm ) with areas of necrosis and hemorrhage involving almost the entire lower lobe was present . the mass seemed to involve the medial aspect of the lobe including the hilar area with some residual remnant of parent lung in the periphery [ figure 1 ] . cut section of the excised tumor reveals a fleshy mass with areas of hemorrhage and necrosis microscopy revealed a cellular unencapsulated neoplasm with tumor cells in vague lobulated sheets with pushing margins [ figure 2a ] . in most areas , the cells appeared small and round with round to ovoid nuclei and a small amount of eosinophilic cytoplasm [ figure 2d ] . in only a few areas was their some degree of spindling with cells growing in fascicular arrays [ figure 2c ] . in places , the cells were in nests separated by fine branching staghorn or hemangiopericytomatous type blood vessels [ figure 2b ] . the differential diagnosis considered based on an initial histology included a neuroendocrine tumor , ewing 's sarcoma , peripheral neuroectodermal tumor ( pnet ) , solitary fibrous tumor , and poorly differentiated synovial sarcoma . photomicrographs of the neoplasm showing ( a ) fairly monomorphic tumor cells in vague lobulated sheets with pushing margins ( h and e , 100 ) , ( b ) fine branching blood vessels separating the tumor nests ( h and e , 200 ) , ( c ) areas of spindling and fascicular array ( h and e , 200 ) , ( d ) monomorphic poorly differentiated round cells in sheets with brisk mitosis ( h and e , 400 ) immunoperoxidase studies on paraffin embedded tissue revealed the neoplastic cells to be focally reactive with antibodies to pancytokeratin along with reactivity for epithelial membrane antibody in approximately 25% of the cells . they failed to react with antibodies to thyroid transcription factor 1 ( ttf-1 ) , synaptophysin , smooth muscle actin , s100 protein , cam5.2 , cd99 , chromogranin , cd45 and cd34 . with the above ihc findings , a poorly differentiated synovial sarcoma was considered most likely and a tle-1 stain was carried out , which revealed diffuse nuclear reactivity of the tumor cells [ figure 3 ] . the patient was subjected to chemotherapy ; however , over the next 4 months , he developed extensive metastatic disease and eventually succumbed to his illness . immunohistochemical profile shows ( a ) focal positivity for pancytokeratin ( b ) more reactivity for epithelial membrane antibody ( c ) cd34 highlights the hemangiopericytomatous pattern of the blood vessels with the negative reaction of the tumor cells . ( d ) tumor cells show diffuse nuclear positivity for transducer - like enhancer of split - 1 ( dab , 200 ) a primary pulmonary synovial sarcoma , even if exhibiting its classic biphasic histology , poses diagnostic problems in the lungs because of the possibility of entrapped pulmonary epithelium being misconstrued as epithelial elements of the tumor . poorly differentiated synovial sarcomas are known to further pose a challenge for definitive diagnosis based on microscopy alone . molecular techniques comprising of reverse transcription polymerase chain reaction , in situ hybridization for the syt - ssx fusion gene and karyotyping for t ( x ; 18 ) translocation remain the gold standard for diagnosis , but these are expensive , not easily available at most centers and in some laboratories require frozen sections . lately this provides a new more specific marker for diagnosis of this rare highly aggressive neoplasm . tle-1 is a member of the groucho / tle gene family involved in beta - catenin signaling pathway and encodes a corepressor implicated in neuronal and epithelial differentiation . it has been found to be significantly expressed in synovial sarcomas with a sensitivity of 82% and specificity of 92% . tle-1 in the same study has also been found to be expressed in 8% of solitary fibrous tumors and in 15% of malignant peripheral nerve sheath tumors . ewing 's sarcoma and primitive neuroectodermal tumors have not been reported to react with tle-1 . we encountered a primary round cell tumor in the lung that did not resemble a lymphoma on histomorphology . the differential diagnosis of a ewing 's sarcoma or a pnet , neuroendocrine tumor , and a solitary fibrous tumor were also considered . the patient ; however , succumbed to the rapidly progressive metastatic disease , he developed thereafter . this case highlights the utility of tle-1 in the diagnosis of poorly differentiated synovial sarcomas . we emphasize it as an essential tool in the immunohistochemical laboratory armamentarium especially in centers where molecular techniques are not easily available . these highly aggressive neoplasms when encountered at relatively inaccessible sites like the lungs should be detected at an early stage . a biopsy and further usage of relevant ihc panel inclusive of tle-1 would be an endeavor to aid diagnosis and perhaps promote further research for yet elusive definitive targeted therapy for these neoplasms .
poorly differentiated primary pulmonary synovial sarcomas are rare and challenging for a surgical pathologist to diagnose . 
 although the demonstration of the tumor specific translocation , t ( x ; 18)(p11.2;q11.2 ) or the resultant fusion gene ( syt - ssx ) is the gold standard for diagnosis , this test is not always accessible . 
 we report the use of immunohistochemistry , including transducer - like enhancer of split-1 in the diagnosis of one such tumor in a young individual .