338 J.M. Cha, J.I. Lee, K.R. Joo, et al. Fig. 1. Colonoscopy detected an approximately 13×12 mm yel- lowish, submucosal tumor in the descending colon. It was hard in consistency without ulceration. Fig. 3. Histological findings of the tumor showing positive immu- noreaction for S-100 protein (immunohistochemical stain, ×400). A B Fig. 2. Histological findings of the tumor. (A) The resected tumor was covered with normal mucosa (H&E, ×20). A nested growth of nonuni- form large tumor cells with slightly pleomorphic nuclei (inlet, H&E, ×400). (B) Some granules were positive for periodic acid-Schiff (PAS, ×400). DISCUSSION Recent advances in diagnostic techniques, especially the widespread use of colonoscopy, have enabled clinicians to iden- tify 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 gastroin- testinal 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; how- ever, 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 pro- tein. The additional staining of granular cells for myelin pro- teins 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 com- puterized 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 iden- tified 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 rou- tine medical checkup or investigations for nonspecific gas- trointestinal symptoms, as was the case in the present pati- ent. Johnston et al. (6) also reported that 17 of 20 colorectal GCTs were found incidentally during investigations for hem- orrhoids or routine medical checkup. In other reports (9, 14), rectal bleeding or a positive fecal occult blood test was des- cribed, but it is unlikely that either of these findings was caused by a GCT, which is covered by an intact colonic mu- cosa without ulceration and inflammation. Colorectal GCTs