Adenomatous lesions of the colon are premalignant lesions which have the potential to develop cancer. Therefore adenomas should be resected endoscopically (endo- mucosa resection, EMR). EMR is conducted after submucosal injection of saline which allows to lift the desired lesion prior to resection. In some cases EMR is complicated due to incomplete or failed lifting after the injection of saline. This so- called "non- lifting" sign is a predictor for malignancy of the lesion. Difficult- to- lift polyps are also difficult- to- resect. A higher proportion of these lesions fail to be resected completely using the EMR technique.

Alternatively, an over- the- scope full- thickness resection device (FTRD) can be used in order to resect colonic lesions. The FTRD technique has been described elsewhere (Schmidt et al. Gastroenterology 2014; 147: 740-742.e2). No comparative data exists until now on the performance of FTRD resection compared to standard EMR resection of difficult- to- resect colon adenomas.

In this study the investigators aim to compare the success of FTRD versus EMR of difficult- to- resect adenomatous lesions (≤ 20 mm).

Inclusion Criteria:

• patients ≥ 18 years
• adenomatous lesion 10-20 mm in size with expected difficulties regarding EMR (e.g. "non- lifting sign")

Exclusion Criteria:

• patients < 18 years
• lesions > 20 mm in size
• high risk carcinomas ("deep submucosal carcinoma")
• American Society of Anesthesiologists (ASA) class IV and higher