The goal of this minimally invasive interventional study is to learn if oncometabolic biomarkers, detected in the exhaled breath and blood can identify early-stage gastro-oesophageal cancer in patient at risk for gastro-oesophageal cancer. The main questions this study aims to answer: Are oncometabolites proficient and reproducible enough to function as diagnostic biomarkers? Can these biomarkers identify early-stage gastro-esophageal cancer? Researchers will compare participants with gastro-oesophageal cancer to healthy controls and participants with Barrett's esophagus to detect meaningful differences between the groups. Participants will provide a breath and blood sample during their routine standard of care visits.