a sufficient resection margin is recommended for complete resection of malignant tumors and reduction of the risk of residual tumor or recurrence . especially in patients with adenocarcinoma in the gastrointestinal ( gi ) tract , survival can be affected by tumor recurrence from a microscopic residual tumor in the resection margin . therefore , surgical resection of adenocarcinomas in the gi tract is recommended to close the abdomen after confirmation of the tumor - negative pathologic margin in frozen sections . on the contrary , the interpretation of the pathologic margin in gi sarcomas such as gastrointestinal stromal tumor ( gist ) is controversial . unlike adenocarcinomas , gi sarcomas could show no significant difference in tumor recurrence or survival between the group with a negative pathologic margin and with a positive pathologic margin even though no residual tumor is visible . little is known about r1 resection of gists from a retrospective institutional analysis with a small sample . herein , the treatment strategy for gist will be discussed with the interpretation of pathologic margins . although a tumor - negative pathologic margin is commonly assumed to mean curative endoscopic or surgical resection of the malignant tumor , well - designed prospective randomized data to support this assumption are lacking . however , patients with residual sarcoma due to incomplete resection ( r2 ) show poor clinical outcomes when compared with patients with r0 resection or even a microscopically positive resection margin ( r1 resection ) . a microscopic positive margin has been reported to possibly have no influence on the disease - free survival of patients or even tumor recurrence in gist . in general , limited resection surgical resection should include a margin of at least 1 cm of normal tissue and an intraoperative evaluation of frozen section . in endoscopic resection , a sufficient vertical resection margin can not be achieved for gists , which are located in the muscularis propria layer . as endoscopic submucosal dissection can only dissect the layer beneath the gist , the resection margin may still involve by tumor cells irrespective of the completeness of the resection . if endoscopic full - thickness resection is performed , r0 resection can be achieved as well as surgical resection . a positive resection margin has been reported as ineffective for predicting the recurrence of small gists . in a previous study that evaluated the risk of recurrence in r0 and r1 resection cases , r1 surgical resection was associated with large tumor size and tumor rupture , and the risk of recurrence was associated with tumor rupture . as the interpretation of pathologic margin is influenced by tumor contraction and fixation after resection , it can be affected by various factors during the process of tissue preparation . therefore , r1 resection does not always mean incomplete resection because a false - positive margin may be assessed based on tissue contraction , encapsulation , or tumor rupture . r1 resection is more frequent in endoscopic resection than in surgical resection because a sufficient resection margin is difficult to attain in endoscopic resection . in a recent study that compared endoscopic and surgical resections of gist , r1 resection was more frequent in the endoscopic resection group than in the surgical resection group . however , the recurrence rate with r1 resection in the endoscopic group was low ( 2.9% , 2/69 ) , but not significantly different from that in surgical resection . although the sample size of endoscopic resection cases was not sufficient to demonstrate the safety of r1 resection , it may be proposed that close serial follow - up can be useful if endoscopic resection is performed without evidence of residual tumor in spite of a microscopically tumor - positive resection margin ( fig . 1 ) . these findings are consistent with those of a previous study that concluded that tumor size and not a microscopically tumor - positive margin was associated with disease - specific survival . therefore , serial endoscopic follow - up is recommended for gist cases with r1 endoscopic resection if no residual tumor is evident immediately after endoscopic resection . as residual or recurrent tumor is possible , close follow - up is mandatory for patients who undergo r1 resection . endoscopic complete resection may be achieved for gists , unlike adenocarcinoma , even in cases with tumor - positive pathologic margins . however , close follow - up should be maintained for the detection of local recurrence .
interpretation of the pathologic margin of a specimen from a resected tumor is important because local recurrence can be predicted by the presence of tumor cells in the resection margin . 
 although a sufficient resection margin is recommended in the resection of gastrointestinal adenocarcinoma , it is not usually regarded strictly in cases of mesenchymal tumor , especially gastrointestinal stromal tumor ( gist ) , because the tumor is usually encapsulated or well demarcated , and not infiltrative . 
 therefore , margin positivity is not rare in the pathological evaluation of surgically or endoscopically resected gist , and does not always indicate incomplete resection . 
 although a gist may have a tumor - positive pathologic margin , complete resection may be achieved if no residual tumor is visible , and long - term survival can be predicted as in the cases with a negative pathologic margin .