Endoscopic submucosal dissection (ESD) is an advanced therapeutic endoscopy that allows the resection (removal) of tumours in the colon or anus without the need for open surgery. It uses a thin and flexible tubular instrument called a colonoscope, which is inserted through the anus and a solution is injected submucosally (beneath the mucous membrane) to raise the area affected by the tumour. The tumour is then resected and a tissue sample can be obtained for further laboratory diagnosis. An ESD needs to be carried out by experienced doctors (endoscopists) due to its complexity and technical difficulty.