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Paper text:
primary lung sarcoma is an extremely rare tumor , accounting for less than 0.5% of all lung tumors .
the variety of soft tissue sarcomas reflects the range of the mesenchymal tissues present in the lung .
histological subtypes are differentiated on the basis of immunohistochemical markers , such as vimentin , desmin , actin , cd99 , and epithelial membrane antigen .
as most of the mesenchymal malignant tumors have a benign counterpart and some epithelial tumors have sarcomatoid differentiation ( renal cell carcinoma , melanoma ) , specific histopathological diagnosis including evaluation of the grade of the lesion is very important .
therefore , they must be considered before the diagnosis of primary lung sarcoma is accepted .
such a rare case of primary pulmonary sarcoma diagnosed by computed tomography ( ct ) guided tru - cut biopsy and subsequent immunohistochemistry is being presented here .
a 55-year - old male presented with left - sided pleuritic chest pain for 2 months and progressively increasing shortness of breath with dry cough for 1.5 months .
initially cough was nonproductive ; later it became productive with scanty white mucoid expectoration , but there was no history of hemoptysis .
he smoked 25 bidis daily for last 32 years , i.e. , he was exposed to 8 pack year smoking .
mild pallor was present , but there were no clubbing and palpable cervical and axillary lymph node .
his respiratory rate was 24 breaths / min , pulse rate 108 beats / min , and blood pressure 120/80 mm hg . examination of respiratory system revealed decreased movement of the left side of the chest wall with ipsilateral fullness .
vocal fremitus was diminished and percussion note was dull over all areas of left side .
left - sided homogenous opacity along with contralateral mediastinal shifting was seen on chest x - ray .
a total of 500 ml of pleural fluid was aspirated from the left side and pleural fluid analysis revealed lymphocyte predominant , exudative , hemorrhagic pleural effusion with adenosine deaminase value , 17.5 u / l .
on contrast enhanced computed tomography ( cect ) of thorax a large heterogeneous mass with multiple areas of necrosis , occupying almost whole of left hemithorax was seen along with left - sided pleural effusion [ figure 1 ] .
ct - guided fine needle aspiration cytology ( fnac ) revealed spindle cell neoplasm . on histopathological section of ct - guided tru - cut biopsy
, it was shown that there were sheets of spindle cells with plump nuclei , moderate degree of nuclear polymorphism , and mitotic figures in more than one high power field  suggestive of spindle cell sarcoma [ figure 2a ]
. however , immunohistochemistry revealed that tumor cells expressed epithelial membrane antigen , cd99 , bcl-2 and calponin and were immunonegative for cytokeratin [ figure 2b ] .
cect thorax showing a large heterogenous mass in left lung with ipsilateral pleural effusion ( a ) photomicrograph showing histopathological features of spindle cell sarcoma ( h and e stain , 100 ) .
synovial sarcoma is a rare mesenchymal tumor , accounting for 10% of all soft tissue tumors .
it occurs most commonly in adolescents and young adults , in soft tissues of the extremities , but lung is also involved .
it is a highly aggressive malignant neoplasm , with a slight male predilection , and is not related to cigarette smoking .
the diagnosis of primary pulmonary synovial sarcoma requires clinical , radiological , pathological , and immunohistochemical investigations to exclude alternative primary tumours and metastatic sarcoma .
primary pulmonary synovial sarcomas are of four subtypes  monophasic fibrous ( spindle ) , monophasic epithelial , biphasic , and poorly differentiated , monophasic subtype being most common .
diagnosis of biphasic subtype is easy as both , epithelial and spindle cell components are present .
close differential diagnoses of monophasic subtype are fibrosarcoma , hemangiopericytoma , leiomyosarcoma and spindle cell variant of squamous cell carcinoma , as all are spindle cell neoplasms .
hence , to differentiate monophasic subtype of synovial cell sarcoma from others , immunohistochemistry is essential .
our case was characterized by the presence of spindle cell sarcoma on histopathological examination , the tumor cells being negative for cytokeratin , but positive for epithelial membrane antigen , cd99 , bcl-2 and calponin .
a total of 66% of primary pulmonary synovial sarcomas are centrally located and presents with post - obstructive pneumonia , atelectasis , and hemoptysis .
peripheral tumors are less common and usually asymptomatic , but may infiltrate adjacent pleura , thoracic wall , and mediastinum , or metastasize to hilar or mediastinal lymph nodes , adrenal , brain , and spinal cord . in our case ,
adjacent pleura was infiltrated by the tumour , resulting in ipsilateral pleural effusion , but there was no distant metastasis .
polymerase chain reaction ( rt - pcr ) helps to differentiate monophasic and biphasic form .
synovial sarcoma is characterized by a reciprocal chromosomal translocation ( x;18 ) ( p11.2 ; q11.2 ) which results from fusion of syt gene on chromosome 18 to either of two genes , ssx 1 and ssx 2 on chromosome x. syt  ssx 1 gene is associated with biphasic subtype and prognosis is bad , whereas monophasic subtype may have either one of two fusion transcripts , syt  ssx 1 or syt  ssx 2 .
all tumors with syt  ssx 2 gene show monophasic morphology . despite its high sensitivity , molecular testing is not required , if the diagnosis of synovial sarcoma is certain or probable on the basis of clinical , histological , and immunohistochemical evaluations .
extensive clinical examination , followed by full body ct scan was done to exclude primary synovial sarcoma located peripherally and distant metastases .
hence surgical excision was planned , but the patient refused to continue treatment further and was lost to follow - up .
primary pulmonary synovial sarcoma is an extremely rare tumor . 
 the diagnosis is established only after sarcoma like primary lung malignancies and metastatic sarcoma have been excluded . 
 it has four subtypes : monophasic fibrous , monophasic epithelial , biphasic , and poorly differentiated subtypes , we report a case of a 55-year - old man , who complained of left - sided chest pain and shortness of breath , had a large heterogeneous mass , occupying most of left hemithorax , associated with ipsilateral pleural effusion , seen on contrast enhanced computed tomogram of thorax . computed tomography guided tru - cut biopsy revealed spindle cell sarcoma . on immunohistochemistry , tumor cells expressed epithelial membrane antigen , cd99 , bcl-2 and calponin and were immunonegative for cytokeratin . 
 so , final diagnosis was primary pulmonary synovial sarcoma , primary pulmonary synovial sarcoma is a rarely reported case of malignant neoplasm of lung . 
 histopathology , immunohistochemistry , and cytogenetics , if possible , are essential for confirmation of its diagnosis .