A 43-year-old woman presented with a gastric subepithelial tumor incidentally detected during screening endoscopy (Fig. 1A). On follow-up endoscopy 6 months later, the tumor was seen at the posterior wall of the lower body and had increased in size compared with measurements obtained from the previous endoscopy; however, no erosion or ulceration was noted (Fig. 1B). When pressed upon with biopsy forceps, the tumor was found to be hard and unmovable. On endoscopic ultrasonography, the tumor measured 1.5 cm and had a heterogeneously hypoechoic appearance in the deep mucosal and submucosal layers (Fig. 1C). An examination of the specimen obtained from endoscopic biopsy revealed only chronic gastritis. Because the size of the tumor had increased, suggesting malignancy, endoscopic submucosal dissection was performed (Fig. 1D).