INTERACT Stomach-II

Inclusion Criteria: * Histologically confirmed gastric cancer or gastroesophageal junction adenocarcinoma * Pathologically and clinically confirmed diagnosis of macroscopic peritoneal metastases (defined as PCI score ≥ 1) * WHO-performance score of 0 to 1 with a life expectancy greater than or equal to three months * Aged 18 years or older * Written informed consent according to the ICH-GCP and national/local regulations Exclusion Criteria: * Distant metastases other than peritoneal metastases or metastatic lymph nodes * Prior palliative systemic therapy for gastric cancer * Prior (neo)-adjuvant systemic therapy for gastric cancer within the six months before enrolment in this study * Severe symptomatic ascites requiring monthly recurrent therapeutic paracentesis * Homozygous dihydropyrimidine dehydrogenase (DPD) deficiency * Any contra-indication for the (planned) systemic chemotherapy (e.g. active infection, serious concomitant disease, severe allergy, persistent neurologic toxicity after (neo-)adjuvant oxaliplatin based systemic therapy), as determined by the treating medical oncologist * Inadequate organ functions (defined as a hemoglobin \<5.0 mmol/l, an absolute neutrophil count \<1.5 x 109/l, platelet count \<100 x 109/l, creatinine clearance \<30 ml/min, bilirubin \>2x ULN and liver transaminases \>2.5x ULN) * Pregnant or lactating women * Concomitant participation in any clinical study that could modify the outcomes relevant to this study * Absence of assurance of compliance with the protocol