Barrett's oesophagus. Endoscope view of the lower part of the oesophagus (gullet) of an 85 year-old male patient. This condition has resulted due to chronic acid reflux from the stomach (not seen). Cells lining the oesophagus have changed into cells similar to those which line the stomach, a type of change known as metaplasia. Here, stomach lining cells are red and the normal oesophageal lining is pink. This condition often develops into an ulcer or even a malignant tumour (adenocarcinoma). Management of this condition is difficult and therefore requires frequent monitoring.