<prompt> A patient with chronic gastroesophageal reflux disease developed Barretts esophagus. Microscopy of this region of esophagus shows:Intestinal dysplasiaGastric metaplasiaSquamous metaplasiaColumnar metaplasia  <response>: Barretts esophagus is specialized columnar metaplasia that replaces the normal squamous mucosa of the distal esophagus in some persons with GERD. Barretts epithelium is a major risk factor for adenocarcinoma of the esophagus and is readily detected endoscopically, due to proximal displacement of the squamocolumnar junction. Ref: Wong-Kee-Song L.M., Topazian M. 2012. Chapter 291. Gastrointestinal Endoscopy. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo Eds, Harrisons Principles of Internal Medicine, 18e. 