Complete Closure After Endoscopic Mucosal Resection of Large Non-Pedunculated Colorectal Polyps

This trial is an open-label, two-arm, parallel-group, multicenter, randomized controlled superiority trial. Patients undergoing EMR will be randomized in a 1:1 ratio and assigned to undergo no closure (control group) vs complete defect closure (experimental group). Participants with planned EMR procedures will be approached by a research assistant before the EMR to request study participation. To mitigate loss to follow-up, patients will be questioned on their preferred contact method with multiple contact methods obtained to adequately reach patients. The importance of follow-up after EMR to detect and treat recurrence will also be highlighted both verbally and in the consent forms during initial patient contact. Despite being experienced, all endoscopist participants will review dedicated teaching videos showing the standardized EMR approach. Videos demonstrating key technical details defect closure will also be circulated across sites to ensure a standardized approach for both procedures as described in the literature. \- Control group: EMR will be performed as per standard of care with submucosal injection and electrocautery resection of all visually visible polyp tissue using a snare. After performing EMR with thermal ablation, prophylactic defect closure will not be performed. Endoscopists can chose to close defects if there are significant concerns for risk of perforation or active perforation after EMR. When the endoscopist determines that the resection is complete, a tattoo will be placed 3 cm distal to the resected lesion to allow for better identification of the resection site in case of follow-up colonoscopy for delayed bleeding. If multiple large polyps are found and removed, the largest lesion (study polyp) will be marked with two tattoos 3 cm distal and 3 cm proximal to the lesion, to clearly identify the study polyp resection site. \- Experimental group: EMR will be performed as per standard of care with submucosal injection and electrocautery resection of all visually visible polyp tissue using a snare. After performing EMR with thermal ablation, prophylactic defect closure will be performed. The choice of the number and types of closure devices used to achieve defect closure will be left to endoscopist discretion. If multiple large polyps are found and removed, the largest lesion (study polyp) will be marked with two tattoos 3 cm distal and 3 cm proximal to the lesion, to clearly identify the study polyp resection site. As per standard of care, endoscopists will take a photograph of the lesion before resection for documentation; a photograph of the EMR resection site will be taken before and after defect closure; a photograph of the defect will be taken if emergency colonoscopy is performed to treat delayed bleeding. When more than one lesion meeting inclusion criteria is present in a patient, all lesions 20mm or larger will be photographed next to an open snare to aid in size measurement. \- 6-month \& 18-month follow-up colonoscopies: To mitigate loss to follow-up, patients will be questioned on their preferred contact method with multiple contact methods obtained to adequately reach patients. The importance of follow-up after EMR to detect and treat recurrence will also be highlighted both verbally and in the consent forms during initial patient contact. Patients will be sent a reminder that they will soon receive an invitation to undergo follow-up through their preferred contact method. If patients do not undergo follow-up after invitation, a research assistant will contact patients by phone to answer any concerns they might have at that time. At follow-up colonoscopies, endoscopists will identify the resection scar tangential to the tattoo placed at the initial EMR. The resection scars will be observed under white light and digital chromoendoscopy to assess for visual recurrence. For all patients, four random biopsies will be taken at the resection scar. If visual recurrence is present, the lesions will be resected using the method deemed most appropriate by the endoscopist at the time and pathologically evaluated for histologic recurrence.