CIRCULATing Biomarkers for Individualized Surgical Therapy in gastroEsophageal Cancer - Phase 1 (CIRCULATE1) (https://classic.clinicaltrials.gov/ct2/show/NCT04455282) is a collaboration project with the Department of General, Visceral, Tumor, and Transplantation Surgery (Univ.-Prof. Dr. med. Christiane Bruns), and) aims to assess the utility of liquid biopsies for therapeutic decision-making in esophageal adenocarcinoma. The phase 1 of the project explores the impact of sampling sites (tumor draining vs. peripheral vein) on the detection of circulating tumor cells (CTCs) and tumor-derived extracellular vesicles (EVs), as well as cell-free circulating tumor DNA (ctDNA). This initial phase is supported by the Brigitte und Dr. Konstanze Wegener-Stiftung.