This study investigates the prognostic role of liquid biopsy in patients with locally advanced gastric cancer. Liquid biopsy for the detection of circulating tumor DNA will be performed: * In the peritoneal lavage, during staging laparoscopy (if indicated) and during curative gastrectomy * In plasma, before staging laparoscopy (if indicated), before curative gastrectomy, at hospital discharge, three months after surgery/at the end of adjuvant therapy, and in case of disease recurrence. The aim of this study is to determine the predictive power of liquid biopsy on overall survival and disease free survival.