This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
[{'content': "A patient with chronic gastroesophageal reflux disease developed Barrett's esophagus. Microscopy of this region of esophagus shows: \nSelect and explain. \nA. Intestinal dysplasia, B. Gastric metaplasia, C. Squamous metaplasia, D. Columnar metaplasia", 'role': 'user'}, {'content': "Answer: D \nExplanation: Barrett's esophagus is specialized columnar metaplasia that replaces the normal squamous mucosa of the distal esophagus in some persons with GERD. Barrett's 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), Harrison's Principles of Internal Medicine, 18e.", 'role': 'assistant'}]