Barrett's oesophagus, endoscope view. This is a condition in which cells lining the lower part of the oesophagus change, a process called metaplasia. It is caused by chronic acid reflux, where stomach acids escape into the oesophagus and cause heartburn. Over time, the squamous cells are replaced by columnar cells (dark red), 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.