Brief Title : Optimized Endoscopic Submucosal Dissection With Snaring for Colorectal Neoplasm

This study is aimed to analyze the outcomes after conventional endoscopic submucosal dissection (ESD) and optimized ESD with snaring (oESD-S) for colorectal neoplasm that is more than 20 mm in diameter of laterllay spreading tumor or flat elevated lesion without stalk. Optimized ESD with snaring means submucosal dissection followed by snaring when narrowed circumference of the remained submucosal tissue beneath the lesion is less than 5 mm in diameter with snaring, then resected by using an electric current. The investigators expect optimized ESD with snaring can provide more time-saving procedure with comparable en-bloc resection rate and perforation rate, when compared with the conventional ESD method.