The global aim of this multi-centric study is to assess the learning curve of U-EMR by an endoscopist skilled in C-EMR aiming to assess the application in real world and check the rate of complete EMR and adverse events related to the procedure.

Conventional Endoscopic mucosal resection (C-EMR) is currently the standard therapy for the removal of large colon polyps. The procedure consists on the injection of fluids into the submucosa layer below the lesion with the intention to create a cushion to separate it from the muscular layer and avoid its damage and consequently perforation and thermal injury. There are some drawbacks about this technique such us fibrotic polyps, difficult location (areas behind the fold and appendicular orifice) and recurrence rate which without ablation techniques could reach 30%.

Underwater endoscopic mucosal resection (U-EMR) has been first described in 2012 by Binmoeller et al [10] and the main difference to C-EMR was the absence of need the submucosal injection. This would be possible because when the lumen is filled with water, the mucosal and the submucosal layer tend to float while the muscularis propria maintains its circular shape even in the presence of peristalsis. Recent data as shown not only a lower rate of recurrence but also a lower procedure time and R0 resections with no difference in adverse events.

Therefore, the global aim of this multi-centric study is to assess the learning curve of U-EMR by an endoscopist skilled in C-EMR aiming to assess the application in real world and check the rate of complete EMR and adverse events related to the procedure.

Inclusion Criteria:

• Age: 18 years-old or older with at least one large (>10 and <30 mm) non pedunculated polyp
• Agreement with study's procedures, having signed the informed consent for the study and EMR, prior to the procedure

Exclusion Criteria:

• Previous attempted resection
• Lesion located at ileo-cecal valve or appendiceal orifice
• Fully circumferential lesion
• Pedunculated polyps (Paris classification type Ip) and ulcerated depression lesions (Paris classification type III)
• Surface pattern suggestive of deep invasion (ex: narrow-band imaging (NBI) International Colorectal Endoscopic (NICE) classification type 3 criteria, Kudo V or equivalent)
• Invasive cancer at EMR specimen
• Inflammatory bowel disease
• Familial polyposis syndrome