The term adenocarcinomas of the esophagogastric junction refers to a specific subtype of cancer affecting the esophagus. Another important type is squamous cell carcinoma. Under normal circumstances, the esophagus is lined with squamous epithelium, which provides high mechanical durability. However, it is not very resistant to the effects of stomach acid. Under the influence of a long-standing reflux disease, which is the abnormal backflow of stomach acid into the esophagus, manifesting as heartburn, the squamous epithelium is transformed into gastric-like epithelium. This transformation is called Barrett's metaplasia. Distinct areas of adenomatous epithelium develop.