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.

Inclusion Criteria:

1. Voluntary written informed consent of the participant or their legally authorized representative has been obtained prior to any breath or blood analysis
2. >18 years old
3. Barrett's esophagus or treatment naïve gastro-esophageal cancer stage I to IV
4. Voluntary healthy controls

Exclusion Criteria:

1. <18 years old

2. Patient has history of:

   1. Active other cancer than gastro-esophageal cancer
   2. Prior cancer treated <3 years ago
   3. Hepatic dysfunction/liver failure (MELT >7)

3. Any disorder, which in the investigator's opinion might jeopardise participant's safety or compliance with the study plan.

4. Insufficient/unreliable quality of breath (e.g., breath flow) or plasma sample (e.g., haemolytic sample)

5. Incarcerated individuals

Data will be shared upon reasonable request with the principal investigator.