Endoscopic Submucosal Dissection for Large Colorectal Tumors Takashi Toyonaga, Eisei Nishino, Akira Hayashibe, Takashi Hirooka Background: The development of endoscopic submucosal dissection (ESD) has enabled en-bloc resection of large colorectal tumors. However, ESD is associated with a high level of technical difficulty and a high incidence of complications. In our department, ESD has been applied to lesions larger than 20 mm in diameter since June 2002, and we have obtained good results by choosing therapeutic instruments according to the situation. Methods: We studied 102 colorectal lesions in 98 patients (62 adenomas, 29 intramucosal cancers and 11 submucosal cancers) undergoing ESD in our department between June 2002 and November 2004. The locations: 13 lesions in the cecum, 28 in the ascending colon, 11 in the transverse, 4 in the descending, 15 in the sigmoid, and 31 in the rectum. Resection method: Erbotome ICC 200 was used for a electro-surgical unit, and a 4-mm length attachment was put on the endoscope tip in order to treat as below. Fourfold diluted hyaluronate sodium was locally injected into the submucosal layers, and the marginal mucosa around the lesions were incised with a Flex knife. Then, a Flex knife was mainly used, but a precutting knife for fibrotic targets and a Hook knife for the situations that muscle layers were located in front were appropriately combined in order to dissect the submucosal layers. When it was difficult to maintain the good endoscopic view, a small caliber-tip transparent hood was used. Results: The diameter of tumors: 13-104 mm (median 28 mm), the diameter of resection specimens: 20-114 mm (median 38 mm), En-bloc and complete resection rate: 96.1% (98/102). With 4 lesions (3.9%) for which en-bloc resection could not be performed, complete fractionated resection was performed after mucosal incision of the entire circumference. Operation time: 16-248 min. (median 42 min). Complications: intra-operative perforation 2.0% (2/102), delayed perforation 1.0% (1/102). The intra-operative perforations were shaped like a pinhole and were conservatively cured by clipping. The delayed perforation required surgery, and it was considered from the resection specimen that the perforation was due to necrosis of the muscle layer by electric current. Intra-operative bleeding with difficulty in hemostasis and post-operative bleeding requiring hemostasis were not observed. Conclusions: We obtained good results in resection by using ESD for large colorectal tumors. Combined therapeutic instruments were useful.