Abstract and Introduction
Barrett's esophagus is an acquired metaplastic abnormality in which the normal stratified squamous epithelium lining of the esophagus is replaced by an intestinal-like columnar epithelium. While in itself a benign and asymptomatic disorder, the clinical importance of this relatively common condition relates to its role as a precursor lesion to esophageal adenocarcinoma, the incidence of which has dramatically increased in Western populations in recent years. Although known to arise as a consequence of chronic gastroesophageal reflux, the cellular and molecular mechanisms underlying development Barrett's esophagus and its progression to cancer remain unclear.
Barrett's esophagus is an acquired metaplastic abnormality in which the normal stratified squamous epithelium of the esophagus is replaced by an intestinal-like columnar epithelium containing goblet cells (intestinal metaplasia) (Fig. 1). The condition is widespread and confers upon sufferers a 100-fold increased risk of developing esophageal adenocarcinoma (EAC). The progression of Barrett's esophagus to EAC is a multistep process in which the metaplastic epithelium is thought to sequentially develop low-grade dysplasia (LGD), high-grade dysplasia (HGD), early EAC, and eventually, invasive carcinoma.
Structure of the luminal lining of the normal esophagus and Barrett's esophagus. Luminal surface of the esophagus is normally lined by a highly-organized stratified squamous epithelium. There is a single layer of basal cells that adhere to the basement membrane, followed by multiple layers of progressively flattened, differentiated squamous cells. Underlying lamina propria contains stromal cells (e.g. fibroblasts: green) and invaginates into the epithelium at regular intervals, producing tall papillary structures. In Barrett's esophagus, which invariable occurs in the distal third of the esophagus, the complex multilayered structure of the normal esophagus is replaced by a single-layered, intestinal-like columnar epithelium containing goblet cells (yellow). Barrett's metaplasia is also characterized by the presence of columnar-lined mucus-secreting glands and inflammatory cells (e.g. mononuclear cells: blue; neutrophils: purple).