- Intervention: instead of standard palliative systemic therapy, patients receive upfront laparoscopic PIPAC with oxaliplatin (92 mg/m2) and simultaneous intravenous bolus 5-fluorouracil/leucovorin (400/20 mg/m2), intentionally repeated with an interval of six weeks until macroscopic intraperitoneal disease progression or laparoscopic non-access. Four weeks after each PIPAC-procedure, patients are radiologically and biochemically evaluated at the oncological outpatient clinic, after which the decision to perform a further PIPAC is made between the treating physicians. In case of intraperitoneal disease progression or unfitness for laparoscopy, patients intentionally receive standard palliative systemic therapy, while further PIPAC-procedures are cancelled. In case of systemic disease progression with intraperitoneal disease response or stable disease, patients intentionally receive standard palliative systemic therapy, while further PIPAC-procedures are intentionally continued until intraperitoneal disease progression, unfitness for laparoscopy, or laparoscopic non-access. See section 'Arms and interventions' below for detailed information on the intervention.