OPPOSITE: Outcome Prediction of Systemic Treatment in Esophagogastric Carcinoma

Inclusion Criteria: Histologically confirmed, resectable adenocarcinoma of the GEJ (type I-III) or the stomach (cT2, cT3,cT4, any cN category, M0), or any cT cN+ M0 with the following specifications: * ECOG-Score ≤ 2 * Patient is fit to undergo surgery (either subtotal or total gastrectomy, transhiatal or abdominothoracic esophagectomy) * No preceding cytotoxic or targeted therapy * No prior partial or complete tumor resection * Exclusion of distant metastasis by CT or MRI of thorax and abdomen, and optionally bone scan (if osseous lesions are suspected due to clinical signs) Exclusion Criteria: * Patients with distant metastasis * Known hypersensitivity against components of the neoadjuvant systemic treatment * Documented history of congestive heart failure NYHA ≥III, myocardial infarction within the past 3 months before the start of neoadjuvant treatment * Uncontrollable high-risk cardiac arrhythmia, e.g. significant ventricular arrhythmia * Past or current history of other malignancies not curatively treated and without evidence of disease for more than 5 years, except for curatively treated early stage cancers such as basal cell carcinoma of the skin and in situ carcinoma of the cervix or the bladder.