granular cell tumors ( gcts ) are relatively rare and thought to be both clinically and histologically benign . although it may arise virtually anywhere in the gastrointestinal tract , the occurrence of gcts in the colon is uncommon ( 1 , 2 ) . instead , these tumors tend to be found incidentally during colonoscopic examinations performed for other reasons , as they are frequently asymptomatic . endoscopically , a gct usually appears as a small submucosal nodule , measuring less than 2 cm in diameter ( 2 - 5 ) . in the present report , we describe a rare case involving a 41-yr - old man diagnosed with a gct arising in the descending colon . the tumor was resected by endoscopic mucosal resection ( emr ) for histological confirmation and treatment . in addition , we carefully reviewed the english literature for reports of other cases of colorectal gct . a 41-yr - old man underwent colonoscopic examination as part of a routine medical checkup . at the time of colonoscopy , however , two small polyps were detected in the sigmoid colon and rectum . these were polypectomized using a snare , with the biopsy findings showing two adenomas . in the descending colon , a yellowish polypoid lesion , 1312 mm in diameter and consisting of a firm nodule covered by intact mucosa , a submucosal tumor , such as a carcinoid tumor , was suspected and the lesion was resected by emr for histological confirmation and treatment . after injection of 4 ml of 3% hypertonic saline solution with epinephrine into the submucosa around the lesion for lifting , the tumor was cut electrically with a high - frequency snare . histological examination of the resected specimen revealed a submucosal tumor composed of plump histiocyte - like cells with an abundant granular eosinophilic cytoplasm positive for acidophilic periodic acid - schiff ( pas ) staining ( fig . the resected tumor was diagnosed as a gct of the descending colon . during 7 months recent advances in diagnostic techniques , especially the widespread use of colonoscopy , have enabled clinicians to identify small and asymptomatic colorectal tumors . gct is a rare tumor that usually appears as a solitary , small , nodular growth and it follows a benign course . while gcts may occur at any site of the body , they are most frequently detected in the oral cavity , skin , and subcutaneous tissue ( 1 ) . in the gastrointestinal tract , where gcts are uncommon , the esophagus is the most frequent site , followed by the colon and stomach ( 1 , 6 ) . as lack et al . ( 1 ) noted in their review , gct was first described in 1926 by abrikossoff as a myogenic tumor ; however , subsequent studies favored a schwann cell origin ( 6 , 7 ) . recently , this hypothesis was supported by positive staining of the cytoplasm and nuclei of granular cells for s-100 protein . the additional staining of granular cells for myelin proteins and myelin - associated glycoproteins provided further evidence . in light of our findings , we reviewed reports of other gcts in the colon and rectum . the reports were identified by a computerized search of the pubmed database ( articles in english between 1992 and 2007 ) and of koreamed ( articles in korean published between 1990 and 2007 ) . fifteen of the cases identified by the computerized search were reviewed ( table 1 ) ( 2 , 5 , 8 - 20 ) . the results showed that most colorectal gcts are asymptomatic and are found incidentally during a routine medical checkup or investigations for nonspecific gastrointestinal symptoms , as was the case in the present patient . ( 6 ) also reported that 17 of 20 colorectal gcts were found incidentally during investigations for hemorrhoids or routine medical checkup . in other reports ( 9 , 14 ) , rectal bleeding or a positive fecal occult blood test was described , but it is unlikely that either of these findings was caused by a gct , which is covered by an intact colonic mucosa without ulceration and inflammation . colorectal gcts may be located anywhere between the rectum and the cecum , with a preferential location in the ascending colon and cecum based on the results of our literature review ( table 1 ) . however , the most common locations for colorectal gcts are the rectum and cecum in the literature including approximately 100 cases of colorectal gcts ( 6 , 11 , 21 ) . colorectal gcts occurred multiply in 10 to 20% of all reported cases ( 5 , 22 ) . endoscopic findings of colorectal gcts are yellow or yellow - white submucosal nodules covered by normal mucosa or sessile polyps , or less frequently , pedunculated polyps ( 1 - 3 , 13 ) . thus , colonoscopists should generally consider the possibility of a gct in the differential diagnosis of a yellowish submucosal tumor of the colon . ( 23 ) reported that the correct diagnosis of gct is seldom made based on macroscopic and endoscopic examinations , even if a diagnosis is made based on the results of endoscopic biopsy , and that these techniques yield a definite diagnosis in only 50% of all patients with gcts . in some cases , endoscopic biopsy finding was misinterpreted as an other diagnosis ( 10 ) . to obtain a definite diagnosis of a submucosal tumor by endoscopic biopsy , it is necessary to sample such tumors either by boring or by performing a jumbo biopsy , and/or if feasible , by carrying out a polypectomy or a mucosal resection . actually , 12 ( 75% ) of 16 patients with colonic gcts in our analysis were diagnosed by polypectomy or emr . endoscopic ultrasonography has recently been applied for evaluating gastrointestinal submucosal tumors , but it may not sufficiently distinguish a benign submucosal tumor , such as a gct , from malignant neoplasia , such as a carcinoid ( 10 , 14 ) . however , it can contribute to planning the endoscopic resection by determining the depth of tumor invasion ( 23 ) . histologically , a gct is composed of a nested growth comprising large tumor cells with ample granular cytoplasm and small round nuclei . the histological findings consist of plump neoplastic cells with abundant granular eosinophilic cytoplasm containing acidophilic , p - aminosalicylic - acid - positive , diastase - resistant granules ; small , uniform nuclei in which mitotic figures are absent ; and neural markers , including s-100 proteins or neuron - specific enolase . granules either arise from autophagocytosis of the cell membrane or represent derivatives of the golgi apparatus ( 24 ) . the histological features of gcts are uniformly expressed and should be adequate to establish the diagnosis ( 1 , 6 - 9 , 19 ) . in our patient , the endoscopic and histological findings of the resected specimen were indeed compatible with gct . few data exist , however , regarding the malignant potential and thus the appropriate management of colonic gct . ( 6 ) also found no evidence of malignant gct in 78 cases of gcts in the gastrointestinal tract and perianal lesions . nonetheless , a malignant variety of gct has been reported ( 25 , 26 ) . the malignant gct seems to be correlated with the size of the tumor since most malignant forms are larger than 4 cm . rapid growth and invasion of adjacent tissue as well as large size were reported to be more indicative of malignant behavior than the histological features . other reported features associated with malignancy include cell necrosis , spindling of tumor cells , cytologic atypia and high mitotic activity , vescicular nuclei with large nucleoli , a high nuclear - to - cytoplasm ratio , and high expression of p53 and ki-67 ( 25 - 27 ) . in our patient , it is usually accepted that endoscopic resection is the best treatment for colonic gcts , since colonic gcts are considered to be usually benign . actually , 12 ( 75% ) of 16 patients in our analysis and 26 ( 79% ) of 33 patients in other report ( 14 ) were successfully treated with polypectomy or emr without complications . although there are no guidelines for the endoscopic treatment of colonic gcts at present , benign lesions < 2 cm in diameter and separated from the muscularis propria can be removed by emr ( 3 , 9 , 14 ) . in our analysis , the remaining four patients underwent surgical resections , based on visualization of the tumors involving the muscularis propria by endoscopic ultrasound , or an incidental intraoperative finding during surgery for another indication . in addition , the treatment may become surgical resection for a benign gct because of the misinterpretation of the biopsied lesion . in surgical cases , colorectal gcts were misinterpreted as a possible adenocarcinoma in the biopsy findings ( 10 ) or not differentiated from a gastrointestinal stromal tumor and a carcinoid with malignant potentials ( 13 ) . although endoscopic resections of colorectal gcts are curative in most cases , local recurrence has also been reported ( 1 ) . neither size , mitotic activity , nor the resection margins are reliable indicators of recurrence . follow - up colonoscopic examination is necessary when the tumors are multiple or a risk of malignancy exists . in addition , endoscopic examination should include a baseline gastroscopy to exclude the presence of gcts in the esophagus and the stomach , which are the other sites in the gastrointestinal tract where gcts can be found . in conclusion , colonoscopists should consider the possibility of gcts in the differential diagnosis of submucosal tumors of the colon as these tumors are increasingly being detected as incidental findings . emr of colonic gct for diagnosis and treatment seems to be feasible and safe , especially when tumors are small .
although colorectal granular cell tumors ( gcts ) are rare , their incidental finding has increased as the use of diagnostic colonoscopy has become more common . here 
 we describe the case of a 41-yr - old man with a gct in the descending colon that was detected after a screening colonoscopy . 
 endoscopic examination revealed a yellowish submucosal tumor , 1312 mm in diameter , in the descending colon . 
 endoscopic mucosal resection ( emr ) followed by histological examination revealed that the tumor was composed of plump histiocyte - like cells with an abundant granular eosinophilic cytoplasm and small round nuclei . 
 the tumor cells expressed s-100 protein and stained with periodic acid - schiff , but were negative for desmin and cytokeratin . 
 the resected tumor was diagnosed as a gct . 
 colonoscopists should consider the possibility of gct in the differential diagnosis of yellowish submucosal tumors of the colon . 
 in such patients , emr seems to be a feasible and safe approach for diagnosis and treatment .