ewing sarcoma / primitive neuroectodermal tumor ( es / pnet ) , previously thought to be separate tumors , is now treated as the same tumor ; both have similar immunohistochemical characteristics and chromosomal translocation . they are malignant tumors composed of undifferentiated small round cells , usually affecting children , adolescents , and young adults . generally es / pnet affects the bones and deep soft tissues , although other organs such as the pancreas , small bowel , esophagus , kidneys , prostate , ovaries , vagina and rectovaginal septum have been reported ; this is termed as extraskeletal es / pnet . to the best of our knowledge , only 5 cases of gastric es / pnet have been reported in the english language literature . a 31-year - old healthy female patient was admitted to the surgical ward due to upper abdominal pain and coffee ground vomiting of 3 days duration . the patient had no other complaints and was hemodynamically stable . rectal examination revealed melena . a nasogastric tube was inserted and revealed coffee ground secretions . upper endoscopic examination revealed a large ulcerated mass located at the lesser curvature of the stomach , with oozing of blood . biopsy revealed tumor cells showing positive immunoreactivity for cd99 ( fig 1 ) , fli1 , vimentin , and ki67 , and negative immunoreactivity for cytokeratin , s100 , cd20 , cd3 , cd79a , pax5 , cd30 , cd43 , dog-1 , cd68 , cd163 , cd33 , mpox , and desmin . es / pnet was suspected and fluorescence in situ hybridization ( fish ) analysis was ordered , which was positive for the ewsr1 gene rearrangement ( 11 : 22 translocation ) . total body computed tomography ( ct ) showed a hypodense mass measuring 9 cm at the lesser curvature of the stomach , with compression on the splenic vein ( fig 2 ) . positron emission tomography - ct ( pet - ct ) revealed pathological uptake of fluorodeoxyglucose at the gastric mass and lymph nodes at the gastrohepatic ligament ( fig 3 ) . the patient refused neoadjuvant treatment , and thus surgery was performed . on exploration of the abdomen , the mass was adhering to the pancreatic tail and mesentery of the transverse and descending colon , along with abnormal pathological lymph nodes at the greater curvature . histopathological examination revealed the mass measuring 11 cm in diameter to be an es / pnet invading the gastric wall , pancreas , and splenic hilum , without involvement of the left adrenal . three years postoperatively , the patient is doing well , with no evidence of disease recurrence . es , a term used to describe tumors that lack neuroectodermal differentiation , and pnet , used to describe tumors that exhibit neuroectodermal features , are now treated as a single entity . tumor cells are rich in glycogen , and pseudorosette formation characterizes the tumor 's morphological differentiation . the diagnosis can be made by immunohistochemical staining for a monoclonal antibody to cd99 ( hba/71 , 12e7 , and 013 ) , which is positive in almost all cases of es / pnet [ 5 , 6 , 7 ] . another immunohistological reagent that can be used for diagnosis is the intermediate filament vimentin , which is usually positive . markers showing variable immunohistochemical staining include s100 , chromogranin a , synaptophysin , and neuron - specific enolase . for tumors occurring in older patients or at unusual sites , fish or reverse transcription polymerase chain reaction can be used for diagnosis [ 3 , 8 ] . these are used to test for the presence of genetic mutation ( 11 : 22)(q24:q12 ) translocation ( ews / fli1 fusion ) , which is an essential criterion for the diagnosis of es / pnet , although sometimes these tests are negative [ 9 , 10 ] . due to the poor results of surgery alone as a treatment modality for extraskeletal es / pnet , the current recommendation is multimodal treatment including surgery , chemotherapy , and radiotherapy . the chemotherapeutical agents used as standard therapy for es / pnet include vincristine , doxorubicin , cyclophosphamide , ifosfamide , and etoposide . of these 5 cases , 3 were females and 2 males , with an average age of 46.6 years ( range 1468 years ) and an average tumor size of 8.5 cm . most of these patients presented with abdominal pain , and 1 presented with an abdominal mass . two cases had hepatic metastasis , 1 had lymph node and peritoneal metastasis , 1 no metastasis , and 1 was not reported . only 2 patients ( of the 3 with metastasis ) herein , we describe the 6th case of es / pnet of the stomach . due to the patient 's refusal of chemotherapeutical treatment three years postoperatively , the patient is doing well , with no evidence of disease recurrence . primary gastric es / pnet is a very rare tumor , and few cases are reported in the literature . due to its rarity , written informed consent was obtained from the patient for publication of this case report and accompanying images ; it is available for consultation . they confirm that the manuscript has not been published elsewhere and is not under consideration by another journal .
ewing sarcoma / primitive neuroectodermal tumor ( es / pnet ) is a tumor of small round cells arising in skeletal tissues . 
 these tumors rarely arise in the stomach . 
 we present a 31-year - old healthy female patient who was admitted to our surgical ward due to upper gastrointestinal hemorrhage . 
 upper endoscopy revealed a large ulcerated bleeding mass originating from the lesser curvature . 
 biopsy revealed tumor cell immunoreactivity positive for cd99 , vimentin , and ki67 ( an index of proliferation ) . 
 these findings were compatible with gastric es / pnet . 
 the fluorescence in situ hybridization analysis result for the ewsr1 gene rearrangement ( 11 : 22 translocation ) was positive . 
 the patient refused neoadjuvant treatment and thus underwent an operation during which a mass at the lesser curvature of the stomach was found . 
 the mass was adhering to the pancreatic tail and to the mesentery of the transverse and descending colon . 
 total gastrectomy , distal pancreatectomy , splenectomy , and left adrenalectomy were done . 
 the patient refused adjuvant treatment . 
 she is free of disease 3 years after surgery .