Inclusion Criteria:  Patients with diagnosis of histologically confirmed, potentially resectable adenocarcinoma of the stomach (GC) or the gastric-esophageal junction (GEJ) treated with the standard regimens (5-Fluoro-Uracil or Capecitabine + Oxaliplatin +/- Docetaxel) Participant is willing and able to give informed consent for participation in the study (prospective and retrospective cohort) or Substitutive Informed Consent Declaration Form will be subscribed by the PI for patients that are not reachable Male or Female, aged >18 years Availability of tissue samples and clinico-pathological data for retrospective cohort  Exclusion Criteria:  Age < 18 years Early Gastric Cancer and T2 (if N0) Linitis plastica Positive peritoneal cytology or peritoneal involvement Distant metastases Patient refusal to participate Patient refusal to the use of their own samples for research Patient withdrawing from treatment plan whilst under therapy due to patient co-morbidities or failure to comply with clinical counselling Patients with underlying pathologies rendering sampling of biological material either as endangering patient's clinical status or as unusable Patients with mental illness hindering the capacity to provide precise information in questionnaires or successfully comply with caregiver's recommendations