Introduction Traditional endoscopy removes pedunculated polyps and some sessile polyps, with flat lesions requiring surgery due to safety concerns and technical difficulties.

With modern approaches flat lesions can now be resected throughout the colon, but lesions >20 mm still remain difficult to remove with little literature to help in assessing the upper size limit for safe resection. We aim to assess the feasibility, safety and medium term outcomes of endoscopic resection of large and very large flat colonic polyps in expert hands.

Methods The majority of patients included in this study were tertiary referrals from Consultant Gastroenterologists or Surgeons. Patients are referred due to difficult endoscopic access, lesion size, concerns of cancer risk, or concerns with other endoscopic complication.

A review of a prospective Endoscopic Mucosal Resection (EMR) database, endoscopy records and pathology reports was performed.

All lesions were removed by a single expert endoscopist, using advanced EMR techniques introduced at the start of this study. These include submucosal injection of colloids, multipiece EMR, endoscopic submucosal dissection (ESD), a combination of the two techniques, and Argon Plasma Coagulation ablation when indicated.

Result 117 patients (52 female, 55 male, mean age 70 years) with 117 polyps, of a mean size 44 mm. (range: 20–150 mm) Follow-up is over a mean 1.54 years (0.1–4.7 years). In those undergoing endoscopic treatment, with follow-up, disease is resected in 82%.

7/117patients had procedure associated complication, 5/117 (4%) delayed bleeds managed endoscopically, 1/117 (0.8%) post-polypectomy syndrome managed conservatively, and 1/117 (0.8%) perforation requiring surgery.

In the patients with carcinoma: 5/15 had <submucosal 1 (SM-1) disease with four resected endoscopically and cured, one having surgery with no residual disease. In 10/15 patients depth of invasion was uncertain or had >SM-1 invasion: one declined surgery and nine had surgery with residual local disease found in five patients (4%) (Abstract 014).