This describes and alteration in the lower third of the esophagus that results as a consequence of acid reflux disease. The damage to the esophagus is observed with an upper GI endoscopy, and biopsies or tissue samples are taken for examination under the microscope. This examination can reveal an alteration to cellular structure called Barrett’s Esophagus, where the tissue belonging to the esophagus now resembles tissue found in the small intestine. This is considered a precursor to potential esophageal cancer. It is important that a patient with Barrett’s esophagus has a long-term follow up and, in some cases, that the tissue is removed via endoscopy.