A condition in which the normal lining of the oesophagus (squamous epithelium) changes its character (see METAPLASIA) so that it is at risk of malignant change at some future date. It may be without symptoms or there may be GASTRO-OESOPHAGEAL REFLUX. Patients are advised to have an ENDOSCOPY every 3–5 years and marked precancerous or actual cancerous changes treated by removing the affected lining or ablation by using an electrode to produce high frequency energy to the surface.