Underwater Endoscopic Mucosal Resection as a Salvage Strategy for a Non-Lifting Early Sigmoid Colon Carcinoma After Failed Conventional Endoscopic Mucosal Resection: A Case Report.

Endoscopic mucosal resection (EMR) has been widely adopted as an endoscopic treatment for colorectal tumors. However, in non-lifting lesions, EMR often becomes technically challenging, leading to piecemeal resection or residual tumor. Recently, underwater EMR (UEMR) has been developed as a novel technique that allows mucosal and submucosal layers to float under water, facilitating snare resection without submucosal injection. UEMR has been reported to improve en bloc resection rates and shorten procedure time compared with conventional EMR, and its usefulness has been demonstrated in non-lifting and residual lesions. We encountered a case in which a 78-year-old woman had a small IIa+IIc-type lesion of the sigmoid colon that could not be completely removed by EMR at a previous hospital due to non-lifting and snare slippage, resulting in only partial resection. She was subsequently referred to our hospital for further treatment. At our hospital, UEMR was successfully performed, achieving en bloc resection. Histopathological examination revealed well-differentiated tubular adenocarcinoma with 560 µm submucosal invasion, negative resection margins, and no lymphovascular invasion, thus fulfilling the criteria for curative resection. This case highlights the illustrative and educational significance of applying UEMR, rather than endoscopic submucosal dissection, to achieve a safe and time-efficient curative resection for a small non-lifting colorectal carcinoma. UEMR may represent a potential salvage option in selected EMR-difficult cases, although further accumulation of cases is warranted to clarify its role.