Inclusion Criteria:  Scheduled for an upper endoscopy or had upper endoscopy within past three years Eighteen years of age or older Capable of producing a saliva sample Able to give informed consent For BE patients only: Endoscopic evidence of Barrett's esophagus (at least 1 cm maximal BE length; i.e. Prague classification: any C, M≥1), and intestinal metaplasia present on esophageal biopsies  Exclusion Criteria:  History of head and neck cancer or esophageal squamous cell or gastric cancer History of esophageal or gastric surgery Scheduled to undergo colonoscopy on the day of initial saliva collection Scheduled only for Endoscopic retrograde cholangiopancreatography (ERCP) or Endoscopy ultrasound (EUS) without accompanying standard upper endoscopy on the day of initial saliva collection For BE patients only: History of prior endoscopic therapy for BE except a history of prior Endoscopic mucosal resection (EMR) of focal lesions without subsequent ablative therapy is permitted