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.

Inclusion Criteria:

• colorectal laterally spreading tumor that is more than 20 mm in diameter
• other elevated or flat colorectal neoplasm without stalk, that is more than 20 mm in diameter

Exclusion Criteria:

• colorectal neoplasms that are proven or suspected to be invaded more than submucosal invasion
• colorectal neoplasms that have severe fibrosis beneath the target lesion
• patient's refusal to participate this study
• less than 18 years old
• subjects who cannot consent voluntarily due to the communication difficulty