Key words: adenocarcinoma of the esophagus and esophagogastric junction, neoadjuvant chemotherapy, PET/CT, histopathological response, technique of esophagogastric anastomosis, anastomotic leak, anastomotic stricture Previous studies have shown that preoperative chemotherapy of locally advanced AEG is beneficial only for patients with a good histopathological response, the so-called responders. The aim of the first part of the thesis was to prospectively verify whether positron emission tomography (PET/CT) could be used for early identification of histopathological non- responders, who could be spared ineffective neoadjuvant treatment. Our study did not prove that the early metabolic response, expressed as the percentage change of the consumption of glucosis on PET/CT performed before (PET1) and 12 to 22 days after the start of the first cycle of preoperative chemotherapy (PET2) correlated with the histopathological response in the resection specimen in the entire population of 90 patients. In a post hoc explorative analysis we found the correlation between metabolic and histopathological response in a subgroup of patients with PET2 performed ≤16 days after the start of the therapy, but this hypothesis needs to be prospectively validated. Our study suggests that PET/CT performed after the first...