| Abstract|| |
Primary sarcomas of lung are rare compared to metastatic sarcomas. Herein, we report a rare case of primary pulmonary synovial sarcoma with polypoid endobronchial growth in a 35-year-old lady who presented with cough and dyspnea. A malignant pulmonary tumor was suspected and left pneumonectomy was performed. Grossly, a non-encapsulated polypoidal endobronchial tumor measuring 6 cm in greatest diameter, with a solid, tan-white cut surface was identified. Microscopically, tumor was characterized by a proliferation of oval to spindle-shaped cells arranged in sheets and fascicles. Focal hemangiopericytomatous pattern was noted. Immunohistochemically, tumor cells were positive for vimentin, BCL-2, MIC-2 and calponin and focally positive for pancytokeratin and epithelial membrane antigen. A subsequent molecular analysis performed using reverse transcriptase-polymerase chain reaction with RNA extracted from paraffin-embedded tissue, revealed SYT/SSX1 fusion gene which confirmed the diagnosis of synovial sarcoma. The utility of immunohistochemistry and molecular techniques in diagnosis of such a rare case is stressed and the relevant literature is discussed.
Keywords: Endobronchial growth, primary pulmonary synovial sarcoma, SYT-SSX1
|How to cite this article:|
Kumar R, Menon S, Desai SB, Pramesh C S, Menon H, Jambhekar NA. Primary endobronchial synovial sarcoma confirmed by SYT-SSX1 fusion gene transcript by reverse transcriptase polymerase chain reaction. Indian J Pathol Microbiol 2009;52:520-3
|How to cite this URL:|
Kumar R, Menon S, Desai SB, Pramesh C S, Menon H, Jambhekar NA. Primary endobronchial synovial sarcoma confirmed by SYT-SSX1 fusion gene transcript by reverse transcriptase polymerase chain reaction. Indian J Pathol Microbiol [serial online] 2009 [cited 2013 May 19];52:520-3. Available from: http://www.ijpmonline.org/text.asp?2009/52/4/520/56147
| Introduction|| |
Primary pulmonary sarcomas are relatively rare compared to metastatic sarcomas and sarcomatoid carcinomas, accounting for less than 0.5% of lung tumors. , Leiomyosarcoma and fibrosarcoma were reported as the most common pulmonary sarcomas, , Synovial sarcoma (SS) is a distinct soft-tissue neoplasm of the extremities in young adults characterized by the presence of specific chromosomal translocation, t(X; 18) (p11.2; q11.2).  SS has been reported in various locations.  Primary pulmonary SS represents a small subset of pulmonary sarcomas, which share similar histomorphological and chromosomal translocations as their soft-tissue counterparts. ,,,, Its recognition is often a diagnostic challenge, because it is likely to be misdiagnosed as either primary pulmonary spindle cell sarcoma/carcinoma or metastatic sarcoma. ,,, Although immunohistochemistry (IHC) is a useful adjunct, it lacks specificity. The utility of molecular techniques to demonstrate the specific chromosomal translocation has increased the sensitivity and specificity of diagnosing SS, especially in unusual locations like the lung. ,
Herein, we present a case of primary pulmonary SS where the diagnosis was confirmed by revealing SYT-SSX1 fusion transcript by reverse transcriptase polymerase chain reaction (RT-PCR).
| Case Report|| |
A 35-year-old non-smoker lady presented with history of cough with mucoid expectoration and dyspnea on exertion for six months. On examination, she had decreased breath sounds and dullness on percussion over the left hemithorax. Computed tomography (CT) scan of the chest revealed a large lobulated mass in the left upper lobe with intrabronchial extension into the left main bronchus with collapse of the lung [Figure 1]. Hilar and mediastinal lymph nodes were enlarged. Bronchoscopy revealed an endobronchial mass lesion in the left main bronchus covered with slough. Bronchial biopsy and bronchoalveolar lavage revealed necrotic material only. A workup for any possible primary lesion elsewhere was noncontributory. She was worked up for surgery and her pulmonary function tests showed adequate reserve. A left pneumonectomy with regional lymph node dissection was performed. She had an uneventful postoperative recovery and was treated with Adriamycin-based chemotherapy. On follow-up, the patient is free of disease one year after surgery.
Grossly, a well-circumscribed, non-encapsulated tumor measuring 6 x 4 x 3.5 cm was noted in the parenchyma of the upper lobe of the left lung with an extension as a polypoidal growth into the left main bronchus. The tumor was abutting the pleura. The cut surface was grey-white, tan, soft to rubbery with focal areas of hemorrhage and necrosis.
Microscopically, a partly circumscribed tumor with focal tongue-like extensions into the interalveolar septae was noted [Figure 2]A. The tumor cells were arranged in either solid sheets or irregular intersecting short fascicles with scanty intervening wiry collagen fibers. Tumor was comprised of closely packed, uniform-appearing ovoid to plump spindly cells, with scant cytoplasm and indistinct cell borders [Figure 2]B. Focal areas of hemangiopericytomatous pattern were noted. Entrapped alveolar epithelium was seen at the periphery of tumor; however, no convincing neoplastic epithelial component was identified. Mitosis was readily evident. Foci of hemorrhage, necrosis and cystic degeneration together with lymphomononuclear inflammatory infiltrate including mast cells were noted. The surgical cut margins and regional nodes were uninvolved. IHC and molecular studies were performed to confirm the diagnosis.
Immunohistochemical stains were performed using an avidin-biotin immunoperoxidase technique with endogenous peroxidase blocking with hydrogen peroxide and antigen retrieval as per company specification and antibody localization with 3, 3'-diaminobenzidine tetrahyrochloride as the chromogen. The various primary antibodies used were pan-cytokeratin (CK;monoclonal,1:100;Dako), vimentin (monoclonal,1:50;Dako), Epithelial Membrane Antigen (EMA;monoclonal,1:100;Dako), MIC-2 (CD99;monoclonal,1:50;Dako), BCL-2 (monoclonal,1:50;Dako), calponin (monoclonal,1:50;Dako), desmin (monoclonal,1:50;Dako), S-100 (polyclonal,1:300;Dako), Smooth Muscle Actin (SMA;monoclonal,1:40;Dako), Neuron Specific Enolase (NSE;monoclonal,1:50;Dako) Thyroid transcription factor-1 (TTF-1;monoclonal,1:50;Dako) and p63 (monoclonal,Clone A4 1:50 Dako).
The tumor cells showed strong immunoreactivity to vimentin, BCL-2 [Figure 2]C, MIC-2 [Figure 2]D calponin and focal reactivity to CK and EMA. IHC for SMA, desmin, NSE, P63 and TTF-1 was negative.
Reverse transcriptase polymerase chain reaction
RT-PCR was performed for detection of t(X; 18) (p11; q11) translocation fusion product. The total RNA was extracted from formalin-fixed, paraffin-embedded neoplastic tissue sections using FFPE RecoverAll total nucleic acid isolation kit from Ambion, Inc. One microgram of total RNA was subjected to reverse transcription using RETROScript kit (Ambion, Inc) protocol. The resulting c-DNAs were PCR-amplified by using SYT 5' forward primer (5' CCA GCA GAG GCC TTA TGG ATA 3') (10 pmoles) in combination with SSX reverse primer (5' TTT GTG GGC CAG ATG CTT C 3') (10 pmoles) to check the presence of SYT/SSX transcript. The conditions used were 94 0 c, 3 min, and 45 cycles of 94 0 c, 50 sec, 61 0 c, 45 sec, 72 0 c, 45 sec and the final elongation at 72 0 c for 5 min. The positive samples were further checked for either SYT/SSX1 or SYT/SSX2 transcript. The primers used were SYT (5' CAA CAG CAA GAT GCA TAC CA 3') (10 pmoles), reverse primer SSX1 (5' GGT GCA GTT GTT TCC CAT CG 3') (10 pmoles) and SSX2 (5' GGC ACA GCT CTT TCC CAT CA 3' ) (10 pmoles). For both, the conditions used were: initial denaturation for 3 min; and then 35 cycles of denaturation 94 0 C, 45 sec; annealing 60 0 C, 1 min; and elongation 72 0 C, 1 min; final elongation at 72 o C for 5 min. The amplified products were run in non-denaturing polyacrylamide gel and stained with silver nitrate. The gel was then documented (Alpha Innotech). The expected band size is 331 bp for both SYT-SSX1 and SYT-SSX2 translocations.
RT-PCR confirmed the diagnosis of SS by demonstration of SYT-SSX1 fusion transcript [Figure 3].
| Discussion|| |
SS is an aggressive neoplasm, accounting for up to 5-10% of soft-tissue sarcomas.  Increasing numbers of reports of primary pulmonary SS are being published at a remarkable rate in recent years mainly due to the use of molecular techniques. ,
The present case is a unique example of primary pulmonary SS presenting as an endobronchial polypoidal growth. Two studies had described such an event previously in the literature. , Although, the exact histogenesis of primary pulmonary SS is uncertain it is hypothesized that primary pulmonary SS might have its origin in pleuripotent mesenchymal cells of bronchial submucosal stromal tissue. 
Primary pulmonary SS shares similar histological features with its soft-tissue counterpart including dense cellularity, interlacing fascicles of short spindly cells with hemangiopericytomatous pattern, intervening wiry collagen, focal myxoid change and mast cell infiltration. ,,,, Several histological variants of SS are known with no difference in the prognosis between these histological subtypes. Primary pulmonary SS is mainly of monophasic fibrous subtype, which is difficult to diagnose and needs to be distinguished from tumors with spindle cell morphology, including both primary lung tumors [such as sarcomatoid carcinoma, sarcomatoid variant of mesothelioma, malignant peripheral nerve sheath tumor, fibrosarcoma, leiomyosarcoma, Ewing's sarcoma, spindle cell thymoma and solitary fibrous tumor (SFT)] as well as metastatic sarcomas. ,, The commonest differential diagnosis is metastatic SS to the lung, which needs to be excluded with a thorough clinical and radiological examination. In the absence of any other primary site, the SS of the lung is considered as the primary. The biphasic subtype is easily identifiable. However, at times entrapped pneumocytes can be mistaken for epithelial component as in our case. They were identified by TTF-1 immunopositivity.
The rare occurrence and overlapping morphologic features prompted the use of ancillary techniques like IHC and molecular studies. In our case, the tumor demonstrated strong and diffuse positivity for vimentin, BCL-2 and MIC-2 and focal positivity for CK and EMA. Occasionally, SS also shows varying degree of immunoreactivity for S100 protein, calretinin, SMA. ,,, BCL-2 expression is nonspecific and can be observed in spindle cell tumors other than SS like SFT. Hence, IHC markers cannot be reliably used to discriminate SS. ,,
Synovial sarcomas are characterized by the specific chromosomal translocation t(X;18) (p11.2;q11.2) which has been detected in more than 90% of SS.  Subsequent cloning of the translocation breakpoint showed that chromosomal translocation t(X;18) (p11.2;q11.2) results in the fusion of the SYT gene from Chromosome 18 to one of three highly homologous genes at Xp11 viz. SSX1, SSX2 and, in rare instances, SSX4. ,, In our case, RT-PCR analysis demonstrated the SYT-SSX1 fusion transcript, confirming the diagnosis of SS. This gene expression pattern is of interest not only in diagnosis but also in predicting the prognosis.  SS with the SYT-SSX1 fusion transcript (irrespective of the histological type) has a poorer prognosis than cases with SYT-SSX2 fusion transcript.  Since there is controversy on this subject additional studies with careful clinical, morphological and molecular correlation, will be necessary to determine the prognostic significance of molecular fusion types in SS.
Primary pulmonary SS behaves more aggressively because of the late presentation, large tumor size and difficulty in achieving free surgical margins. Hartel et al.  had compiled data of five case series of primary pulmonary SS and mentioned that on an average 38% cases showed local recurrences and 42% died of disease within five years. Surgery is the mainstay of treatment and free surgical margins are critical in prevention of local recurrence. The rarity of this tumor has not permitted controlled studies with adjuvant chemotherapy. Adjuvant chemotherapy utilizing ifosamide and adriamycin increases the time for local recurrence and disease-free survival. Nevertheless, the prognosis of primary pulmonary SS remains poor with an overall survival of 50%. 
To conclude, primary pulmonary SS is a rare, aggressive and increasingly recognized subset of intrathoracic sarcomas. This report provides evidence that the application of molecular technique with conventional histology and IHC may allow us to classify some spindle cell malignancies resembling SS in unusual locations where morphologic diagnosis is still undetermined.
| Acknowledgments|| |
The authors thank Dr. Ranjan Basak PhD, Division of Molecular Pathology, Department of Pathology, Advanced Centre for Treatment, Research& Education in Cancer, Kharghar, Navi, Mumbai 410 210, India for performing RT-PCR.
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Department of Pathology, Tata Mmeorial Hospital, Dr Ernest Borges Marg, Parel, Mumbai-400012
[Figure 1], [Figure 2], [Figure 3]