a 47-year - old man with a clinical impression of a submucoal tumor of the stomach detected during the health screening examination visited the samsung medical center for further evaluation of the lesion . a computed tomography scan demonstrated a 2 cm - sized mass with prominent contrast enhancement ( fig . on endoscopy , a 32 cm - sized flat and submucosal tumor - like elevated lesion with mucosal ulceration was found at the mid body , posterior wall and greater curvature side of the stomach ( fig . the tumor cells were composed of spindle and epithelioid cells with oval nuclei and an abundant myxoid stroma rich in small blood vessels ( fig . three mitotic figures were found per 50 high powered fields . in this case , differential diagnoses included neurofibroma , schwannoma , extracardiac myxoma , and gist . on immunohistochemistry , the tumor cells were positive for smooth muscle actin ( sma ) and negative for c - kit , desmin , cd34 ( fig . 2d ) , s-100 protein , protein kinase c ( pkc)-theta , epithelial membrane antigen ( ema ) , and neurofilament . in the differential diagnoses , neurofibroma was excluded because the tumor cells were negative for s-100 protein and neurofilament . gist was excluded due to their multinodular plexiform growth pattern , less eosinophilic cytoplasm , and complete negativity for c - kit , cd34 and pkc - theta . the patient was alive without any recurrence or metastasis of the tumor after being followed up for 6 years . genetic analyses for kit and platelet - derived growth factor receptor alpha ( pdgfra ) genes were wild - type for mutation . a 63-year - old woman with no associated clinical symptom visited korea university guro hospital for a health screening examination . the tissue was processed to formalin fixed and paraffin embedded block and we obtained hematoxylin and eosin stained 4 m sections . microscopically , the tumor was located at the submucosal layer with mucosal ulceration and was relatively well demarcated . in the microscopic examinations , the tumor was composed of loosely arranged spindle cells , myxoid stroma and was rich in small vessels ( fig . the tumor cells showed a bland looking , oval to slightly elongated nuclei without atypia and a faintly eosinophilic cytoplasm . the stroma was abundant in variable shaped small vessels and was positive for alcian blue stain ( fig . 3d ) , but negative for c - kit , cd34 , desmin , s-100 protein ( fig . although some mast cells were noted in the stroma , other inflammatory cells including lymphocytes , neutrophils , plasma cells and eosinophils were inconspicuous . mutation analyses for exon 9 , 11 , 13 , and 17 of the kit genes and exon 12 , 14 , and 18 of the pdgfra genes were performed and the tumor was wild - type for mutation . a 47-year - old man with a clinical impression of a submucoal tumor of the stomach detected during the health screening examination visited the samsung medical center for further evaluation of the lesion . a computed tomography scan demonstrated a 2 cm - sized mass with prominent contrast enhancement ( fig . on endoscopy , a 32 cm - sized flat and submucosal tumor - like elevated lesion with mucosal ulceration was found at the mid body , posterior wall and greater curvature side of the stomach ( fig . the tumor cells were composed of spindle and epithelioid cells with oval nuclei and an abundant myxoid stroma rich in small blood vessels ( fig . three mitotic figures were found per 50 high powered fields . in this case , differential diagnoses included neurofibroma , schwannoma , extracardiac myxoma , and gist . on immunohistochemistry , the tumor cells were positive for smooth muscle actin ( sma ) and negative for c - kit , desmin , cd34 ( fig . 2d ) , s-100 protein , protein kinase c ( pkc)-theta , epithelial membrane antigen ( ema ) , and neurofilament . in the differential diagnoses , neurofibroma was excluded because the tumor cells were negative for s-100 protein and neurofilament . gist was excluded due to their multinodular plexiform growth pattern , less eosinophilic cytoplasm , and complete negativity for c - kit , cd34 and pkc - theta . the patient was alive without any recurrence or metastasis of the tumor after being followed up for 6 years . genetic analyses for kit and platelet - derived growth factor receptor alpha ( pdgfra ) genes were wild - type for mutation . a 63-year - old woman with no associated clinical symptom visited korea university guro hospital for a health screening examination . the tissue was processed to formalin fixed and paraffin embedded block and we obtained hematoxylin and eosin stained 4 m sections . microscopically , the tumor was located at the submucosal layer with mucosal ulceration and was relatively well demarcated . in the microscopic examinations , the tumor was composed of loosely arranged spindle cells , myxoid stroma and was rich in small vessels ( fig . the tumor cells showed a bland looking , oval to slightly elongated nuclei without atypia and a faintly eosinophilic cytoplasm . the stroma was abundant in variable shaped small vessels and was positive for alcian blue stain ( fig . 3d ) , but negative for c - kit , cd34 , desmin , s-100 protein ( fig . although some mast cells were noted in the stroma , other inflammatory cells including lymphocytes , neutrophils , plasma cells and eosinophils were inconspicuous . mutation analyses for exon 9 , 11 , 13 , and 17 of the kit genes and exon 12 , 14 , and 18 of the pdgfra genes were performed and the tumor was wild - type for mutation . pamt of the stomach is a recently described unique gastric mesenchymal tumor that is myofibroblastic in origin with the potential to differentiate toward smooth muscle cells . the diagnosis of pamt is based on the histologic feature , plexiform architecture , an abundant myxoid stroma rich in small blood vessels , and immunohistochemical findings . reported cases reveal features of smooth muscle differentiation and a spectrum of fibrous , fibromyxoid and myxoid stromal features by immunohistochemistry and electron microscopy . to date , only 22 cases have been reported worldwide as " plexiform fibromyxoma,"2 " plexiform angiomyxoid myofibroblastic tumor,"1 and " plexiform angiomyxoid tumor."9 recently , takahashi et al.6 reported that this tumor is not a pure myofibroblastic tumor and may contain tumor cells with a fibroblastic or smooth muscle nature . table 1 summarizes the clinicopathological features of the previously reported cases with an unpublished case and our two pamt cases . to date most tumors occurred in the gastric antrum,6 but they can occur anywhere in the stomach including the fundus8 and body , similarly to our cases . distal or partial gastrectomy , wedge resection and polypectomy were performed for treatment . in all reported 22 cases to date , there was no recurrence or metastasis of disease , although the tumor reached a large size of up to 15 cm in its greatest dimension.8 however , in some cases , the follow - up duration was too short to precisely predict prognosis . although the number of reported pamt cases is small , malignant change , metastasis to adjacent organs , and recurrence or death from the disease have not yet been reported . based on favorable prognoses , absence of nuclear atypia , and low mitotic index , we suggest that pamt can be categorized as a benign lesion . pathologic differential diagnosis of this new disease entity includes gist , inflammatory fibroid polyp , leiomyoma , neurofibroma , schwannoma , extracardiac myxoma , desmoids ( mesenteric fibromatosis ) , solitary fibrous tumor and inflammatory myofibroblastic tumor . histologic characteristics of pamt include a multinodular plexiform growth pattern , bland looking spindle cells , and an alcian blue positive myxoid stromal matrix rich in variable sized small vessels . on immunohistochemistry , the tumor cells of pamt are positive for sma and negative for c - kit , cd34 , s-100 protein , ema , and desmin . these histologic and immunophenotypic features are helpful in diagnosing this rare disease . in our cases , as the tumor cells were ovoid , showed no atypia , and were located in the submucosa and proper muscle layer , the most important differential diagnosis was gist . moreover , compared to tumor cell populations found in gist , the stromal component is prominent and the immunohistochemisty of pamt is clearly differentiated from gist . here , we report two cases of pamt , which has not yet been reported in korea . our report may help increase the awareness of this rare but important new disease entity .
plexiform angiomyxoid myofibroblastic tumor ( pamt ) of the stomach is a recently recognized entity . because of its rarity 
 , only 22 cases have been reported in the english - language literature and most of these are single case reports . 
 we report two cases of gastric pamt . 
 the tumor cells were bland and plexiform arranged in a myxoid stroma , which was positive for alcian blue . 
 immunohistochemically , the tumor cells were positive for smooth muscle actin , but negative for c - kit , cd34 , desmin , s-100 protein , epithelial membrane antigen , neurofilament , and protein kinase c - theta . mutation analyses for exon 9 , 11 , 13 , and 17 of kit genes and 12 , 14 , and 18 of the platelet - derived growth factor receptor alpha ( pdgfra ) genes were performed and the tumors were wild - type for mutation .