The gastroesophageal junction is demarcated by a transition from one epithelial type (nonkeratinized stratified squamous epithelium) to another epithelial type (columnar epithelium). In some people, the histological junction does not lie at the anatomical gastroesophageal junction but occurs more proximally in the lower third of the esophagus. This may predispose these people to esophageal ulceration and is also associated with an increased risk of adenocarcinoma. In certain conditions, like gastroesophageal reflux, the stratified squamous epithelium in the esophagus can undergo metaplasia and the epithelium in the lower esophagus is replaced by columnar epithelium, a condition called Barrett’s esophagus. The presence of Barrett’s esophagus predisposes these people to the development of esophageal malignancy (adenocarcinoma).