These patients will include: 1) patients with known Barrett's esophagus with or without dysplasia, who are scheduled for surveillance endoscopy with biopsy or endoscopic mucosal resection (EMR) 2) patients with early esophageal or gastric cancer who are undergoing confirmatory endoscopy with biopsy or 3) patients with intestinal metaplasia with or without dysplasia of the stomach who are undergoing endoscopy with biopsy or EMR.