Intraperitoneal Paclitaxel and Systemic Therapy Versus Systemic Therapy Alone in Gastric Cancer Patients With Peritoneal Metastasis

Inclusion Criteria: * Gastric or gastro-oesophageal junction Siewert type II or III adenocarcinoma verified by biopsy or cytology from the primary tumour * Peritoneal metastasis verified by biopsy, or cytology from ascites or peritoneal wash fluid * Staging laparoscopy with assessment of peritoneal cancer index (PCI) performed less than four weeks before enrolment. * Patients with tumour positive cytology (CYT+) without clinically manifest peritoneal metastases at baseline (PCI 0) staging laparoscopy can be included if they persist to be CYT+ after at least four cycles of systemic chemotherapy. * Adequate hematology assessment and serum chemistry * Eastern Cooperative Oncology Group (ECOG) performance status 0-1. * Age of at least 18 years * Life expectancy of at least three months * Assurance that adequate anti-reproductive measures will be taken during study interventions when applicable Exclusion Criteria: * Comorbidity that does not allow treatment with ST or IP paclitaxel * Confirmed or suspected severe abdominal adhesions * Severe coagulation disorder which precludes surgical interventions * Distant metastases (including M1 lymph node metastases) other than peritoneal, with the specific exception of ovarian metastases * Symptomatic ascites already requiring drainage for palliation, or expected to require drainage in the short term * Peritoneal recurrence of gastric cancer diagnosed within 6 months after curative intent surgery * Previously received more than 2 cycles of palliative-intent systemic chemotherapy (with the specific exception of cytology positive patients without manifest peritoneal metastases) for the current gastric cancer (up to 2 cycles of first line chemotherapy is allowed). Perioperative chemotherapy within previous curative context is allowed * Another malignancy that can affect survival within the next three years * Known or suspected allergies against any product included in the trial interventions * DYPD deficiency * Pregnancy or recent delivery within 28 days postpartum or ongoing breastfeeding * Active sex-life without use of secure contraceptive method. * If the investigator considers the patient inappropriate for participation in the study for any other reason * Ongoing or recent participation (within 30 days) in a clinical trial with an investigational medicinal product