Validation study of watchful waiting for bleeding after colorectal endoscopic submucosal dissection

Interventions: Determination whether emergency endoscopy is indicated based on the treatment policy for hematochezia after colorectal ESD Primary outcome(s): 1. Receiving blood transfusion 2. Receiving colonoscopy within 48 hours after the end of ESD Study Design: single arm study, open(masking not used), uncontrolled control, single assignment, treatment purpose