Barrett's oesophagus. Light micrograph of a section throught the lower part of an oesophagus (gullet) with Barrett's oesphagus. This is a condition in which the epithelial cells change, a process called metaplasia. It is caused by chronic acid reflux, where stomach acids escape from the stomach into the oesophagus, leading to heartburn. Over time, the normal squamous cells (top left) found in the oesophagus are replaced by columnar cells (top right), similar to those that line the stomach or colon. The condition is considered a precursor of oesophageal cancer. Treatment is with drugs to reduce stomach acid production, although advanced cases may require surgery or cancer treatments.