the tumor is characterized by a variable degree of epithelial differentiation and by translocation t ( x;18 ) ( p11;q11 ) forming a characteristic syt - ssx chimera gene . the tumor develops mainly in the extremities of young adults , but exceptionally in the gastrointestinal ( gi ) tract . her laboratory data showed anemia , and the serum levels of cea and ca19 - 9 were within normal limits . endoscopic examination revealed an elevated lesion in the body of the stomach ( fig . the surface of the tumor was covered with normal mucosa , on the top of which ulcer was noted ( fig . 1b ) . abdominal computed tomography ( ct ) showed an elevated lesion protruding into the luminal side of the stomach ( fig . the tumor was confined to the mucosa , and no tumor was detected in the serosa . endoscopic biopsy revealed the proliferation of spindle cells in the propria , suggesting poorly differentiated adenocarcinoma and carcinosarcoma of the stomach . the patient received no adjuvant therapy , and there has been no evidence of local recurrence ( fig . d there was no local recurrence in the stomach on the follow - up endoscopy endoscopic features of the gastric tumor . a lateral view of the gastric tumor . the resected tumor was 3.5    2.8    1.2  cm in size ( fig . histological examination showed that the tumor was confined from the propria of the mucosa to the submucosal layer of the gastric wall . the tumor was composed of bundles of spindle cells with slightly swollen nuclei , and the spindle cells infiltrated into the propria ( fig . 2d ) , and glandular structures composed of epithelioid cells with atypical nuclei were sparsely mixed ( fig . 2pathological features of the gastric tumor . a the loupe image of the resected tumor . c the tumor cells infiltrated into the propria . d sheet - like proliferation of spindle cells . f , g positive immunostaining for cytokeratin ( ae1/ae3 ) in spindle cells ( f ) and epithelioid cells with glandular structure ( g ) . i 200 ) pathological features of the gastric tumor . a the loupe image of the resected tumor . c the tumor cells infiltrated into the propria . d sheet - like proliferation of spindle cells . e glandular structure with atypical cells was also observed . f , g positive immunostaining for cytokeratin ( ae1/ae3 ) in spindle cells ( f ) and epithelioid cells with glandular structure ( g ) . i 200 ) immunostaining was done on the 4-m - thick paraffin sections by ventana gx system ( roche diagnostics kk , tokyo , japan ) . the antibodies used in this study and the results are summarized in table  1 . 2f ) , and epithelioid cells with glandular structure also showed positive reaction ( fig . 2i).table  1antibodies used in immunohistochemistry and resultsantibody toclonesourcedilutionresultpancytokeratinae1/ae3dako japan1:100+emae29dako japan1:100+vimentinv9dako japan1:300+cd99dako japan1:200+bcl2124dako japan1:50+kitdako japan1:300dog1nichirei , kkprediluted cd34qbend/10ventanaprediluted  desmind33dako japan1:30sma1a4dako japan1:100s100dako japan1:500ki67mib1dako japan1:5020  % 
 ema epithelial membrane antigen , sma smooth muscle actin antibodies used in immunohistochemistry and results 
 ema epithelial membrane antigen , sma smooth muscle actin the syt - ssx chimera transcript was analyzed by reverse transcription ( rt)-polymerase chain reaction ( pcr ) using total rna extracted from paraffin sections . as a control case , total rna was extracted using rneasy ffpe kit ( qiagen , kk , tokyo , japan ) . briefly , two paraffin sections of the tumors were deparaffinized and transferred to 1.5  ml tubes . the tissues were digested with proteinase k solution , and total rna was extracted with a spin column according to the protocol recommended by the manufacturer . complementary dna ( cdna ) was synthesized from 1  g total rna by rt using the superscript iii first strand cdna synthesis system ( invitrogen corp . , a non - rt sample was prepared in the same way except that the reaction was done without reverse transcriptase . the syt - ssx chimera transcript was amplified by pcr using primers syt : 5-cag cag agg cct tat gga tat ga-3 and ssx : 5-tca ttt tgt ggg cca gat gc-3 , which were reported by guillou . cdna transcribed from 100  ng total rna and non - rt sample was used as a template . the amplified product was electrophoresed in agilent 2100 bioanalyzer ( agilent technologies , inc . , the pcr product was subcloned into pcrii vector ( invitrogen corp . ) and sequenced using a bigdye terminator cycle sequencing kit ( applied biosystems , inc . , a single amplified product was obtained in the rt sample of the current case ( fig . no amplification was observed in the non - rt sample of the current case , and in rt and non - rt samples of gastric adenocarcinoma . sequencing of the subcloned fragment revealed that the product was 101 base pairs in length , and sequencing of the product determined that the product is a chimera transcript of syt and ssx1 genes ( fig . bps base pairs , nc negative control , rt reverse transcription , nrt non - reverse transcription . sequencing of the product revealed chimera transcript of syt - ssx1 
  molecular analysis . a rt - pcr of syt - ssx . bps base pairs , nc negative control , rt reverse transcription , nrt non - reverse transcription . the current case presented a localized elevated lesion of the gastric mucosa , resembling a submucosal tumor ( smt ) . the tumor was mainly located in the mucosa and submucosa , and invasion beyond the muscular layer was not found . histologically , the tumor was composed of spindle cells , which showed positive reactions for cytokeratin , ema and cd99 . the final diagnosis of synovial sarcoma was obtained by the demonstration of a chimera transcript of syt - ssx1 by rt - pcr using paraffin sections . , only 13 cases have been reported in the english - language literature ( table  2 ) ; [ 35 ] . this is the first report of a japanese case of primary gastric synovial sarcoma . among the 14 reported cases , the ages ranged from 29 to 68  years , and the mean is 50  years . most of the cases were monophasic subtype , and foci of poorly differentiated component were noted in two cases [ 3 , 4 ] . definitive diagnosis was obtained by intensive immunohistochemical studies and molecular analyses using fluorescence in - situ hybridization ( fish ) and rt - pcr [ 35].table  2reported cases of primary gastric synovial sarcomacaseage / sexlocationsize ( cm)histologytreatmentoutcome167/fbody - antrum0.8monophasic fibrouspartial gastrectomyaned , 12 mo249/mbody2monophasic fibrous , with poorly differentiated componentsegmental / wedge resectionomental metastasis dod , 29 mo368/fbody2monophasic fibrouswedge resectionaned , 22 mo429/mbody2.8monophasic fibrouspartial gastrectomyaned , 224 mo554/fantrum3monophasic fibrousantrectomy/ gastroduodenal resectionnd658/fbody3monophasic fibrouswedge resectionaned , 21 mo737/ffundus4monophasic fibrouspartial gastrectomylocal recurrence doc , 48 mo847/megj5.2biphasicgastrectomy/ partial esophagectomyaned , 21 mo950/mfundus6monophasic fibrousresection  +  chemotherapyalive with recurrence 6 mo1038/fbody7.2monophasicwedge resection + chemotherapyliver metastasis , alive with recurrence , 6 mo1142/mbody8biphasicpartial gastrectomy + chemotherapydod , 25 mo1266/ffundus15monophasic fibrousgastrectomy/ partial esophagectomylost to follow - up1355/fantrum 16monophasic , focally biphasic , with poorly differentiated componenthemigastrectomyliver metastasis dod , 6 mocurrent case46/fbody3monophasicpartial gastrectomyanedcase 17 , 9 , 11 , 12 ; case 8 , 13 , ; case 10 , 
 f female , m male , egj esophagogastric junction , aned alive with no evidence of disease , doc died of other cause , dod died of disease , mo months , nd not described reported cases of primary gastric synovial sarcoma case 17 , 9 , 11 , 12 ; case 8 , 13 , ; case 10 ,  
 f female , m male , egj esophagogastric junction , aned alive with no evidence of disease , doc died of other cause , dod died of disease , mo months , nd not described the spindle cell growth in the gastric wall in our case resembled those of other smts arising in the stomach , such as gastrointestinal stromal tumor ( gist ) , leiomyoma , leiomyosarcoma and schwannoma . the spindle cells were negative for the markers of other mesenchymal tumors ( table  1 ) . in contrast , they showed positive for cytokeratin and ema , as did epithelioid cells with glandular structure , reminiscent of the pathological features of carcinosarcoma . true carcinosarcoma refers a tumor mixed with adenocarcinoma and sarcomatous components with chondroid , osteoid and muscular differentiations . so - called carcinosarcoma is a tumor composed of a bland growth of spindle cells . it should be noted that the most of the reported cases of synovial sarcoma in the stomach exhibited a monophasic pattern ( table  2 ) ; [ 35 ] . the positive reaction for cd99 is a characteristic feature of synovial sarcoma in the soft tissues , as documented in the previous two cases of gastric synovial sarcoma [ 4 , 5 ] and in the current case . translocation of chromosomes t(x;18 ) gives rise to a syt - ssx chimera transcript , which is detected exclusively in synovial sarcoma . for the detection of this gene , fish and rt - pcr are frequently applied to paraffin sections . in the current case , we were able to identify the genetic alteration by rt - pcr , and the fusion of syt and ssx1 was confirmed by sequencing . in the previous studies , 4 cases had syt - ssx1 and 4 cases had syt - ssx2 chimera transcript [ 4 , 5 ] . it was reported that the epithelial differentiation is more prominent and metastasis is more frequent in the synovial sarcomas of the soft tissue with syt - ssx1 . the clinical significance of the genetic alterations of the primary gastric synovial sarcoma needs to be elucidated . compared to gastric carcinosarcoma [ 8 , 9 ] , synovial sarcoma affects slightly younger people . while male predominance was reported in carcinosarcoma , female predominance is noted in gastric synovial sarcoma ( table  2 ) ; [ 35 ] . primary gastric synovial sarcoma follows a favorable course . on the other hand , prognosis of carcinosarcoma is poor , and approximately half of the patients died within 6  months . among these , there are a couple of cases with a relatively favorable prognosis [ 8 , 10 ] . although early surgical treatment is essential for better prognosis , it is speculated that some primary gastric synovial sarcoma might have been diagnosed as carcinosarcoma . accurate distinction between synovial sarcoma and carcinosarcoma is necessary for the determination of postoperative treatment and prediction of prognosis . although the number of cases of primary gastric synovial sarcoma is limited , their histology is not different from those in the soft tissue . it was reported that patients with tumor < 5  cm in size , < 10 mitoses in 1.7  mm and without necrosis follow a favorable course in cases of synovial sarcoma of soft tissue . similarly , in primary gastric synovial sarcoma , four out of six patients with tumor > 5  cm in diameter recurred or died of the disease ( table  2 ) . two patients with poorly differentiated component died of metastatic disease [ 3 , 4 ] . it was also reported that vascular invasion and perineurial invasion could be a risk factor for recurrence and metastasis of synovial sarcoma of soft tissue . hence , pathological diagnosis of primary gastric synovial sarcoma should include the size , mitotic count , the presence or absence of necrosis and poorly differentiated component , vascular and perineurial invasions and the presence or absence of tumors cells at the margin .
a 42-year - old japanese woman complained of upper abdominal pain . 
 endoscopic examination demonstrated an elevated lesion in the body of the stomach , and a biopsy specimen demonstrated proliferation of atypical spindle cells . 
 she underwent partial gastrectomy ; the resected tumor measured 3.5    2.8    1.2  cm in size . 
 histological examination disclosed the haphazard proliferation of spindle cells in the mucosa mixed with less prominent epithelioglandular component . 
 the spindle cells were positive for cytokeratin , vimentin , ema and cd99 , but not for kit , dog1 , desmin or s100 . 
 reverse transcription - polymerase chain reaction using paraffin sections amplified a syt - ssx1 chimera transcript . 
 a diagnosis of synovial sarcoma was made . 
 there has been no sign of recurrence or metastasis for 6  years after the operation . 
 synovial sarcoma in the stomach is very rare . 
 since differential diagnosis of synovial sarcoma from carcinosarcoma and mesenchymal tumors is critical for the treatment and prediction of prognosis , accurate diagnosis with molecular analysis is essential .