Clinical Utility of Circulating Tumor DNA in Gastro-Esophageal Cancer

This is a prospective cohort study designed to evaluate the treatment effect as well as predictive and prognostic factors with special emphasis on the clinical utility of ctDNA in plasma in patients with gastroesophageal cancer. Patients with gastroesophageal cancer are included in 5 separate cohorts scheduled for * Surgical resection + perioperative chemotherapy (cohort 1) * Neoadjuvant chemoradiotherapy followed by surgical resection (cohort 2) * Definitive chemoradiotherapy with curative intent (cohort 3) * Systemic therapy with the intent to prolong survival (cohort 4) * Palliative treatment without the use of chemotherapy (cohort 5)