This trial is to evaluate the safety and efficacy of using MASTER, a novel robotics enhanced endosurgical system to perform endoscopic submucosal dissection (ESD) of gastric/colon cancer in human. The MASTER is a master-and-slave robotic system that is deployed through a standard dual-channel therapeutic endoscope. It introduces robotic control of endoscopic surgical tools and tasks through an ergonomic human-machine interface built around the original endoscopic paradigm. In doing so, it separates control of instrumental motion from that of endoscopic movement such that surgical tasks may be independently executed by a second operator via a human-machine interface. With it, endoscopically deployed instruments can be independently controlled, allowing thus bimanual coordination of effector instruments to facilitate actions such as retraction/exposure, traction/countertraction, approximation and dissection of tissue. Using the MASTER, operational dexterity is increased, thus making it easier for the operator to perform the ESD procedure as compared with using the conventional endoscope. This study will measure the ease of using the MASTER to perform the various surgical tasks involved in the ESD procedure, the time taken to perform the procedure, and record complications, if any, occurred during and after the procedure.