In a multicentric randomized controlled trial, we will compare standard surgery (consisting in removal of the primary cancer) followed by 6 months of adjuvant chemotherapy associated with 3 cycles of oxaliplatin-based PIPAC (4-6 weeks apart), to standard surgery followed by 6 months of adjuvant systemic chemotherapy (routine treatment), in patients with colorectal cancer at high risk for metachronous peritoneal carcinomatosis (pT4 pN0-2 cM0 pMMR colorectal cancer of the colon, colorectal junction or high rectum and/or with positive cytology) in terms of 1-year and 3-year peritoneal metastasis-free survival (as measured by imaging and/or surgical exploration), 1-year and 3-year disease-free survival, as well as 1-year and 3-year overall survival. In terms of outcomes measurement, patients in both groups will benefit from diagnostic laparoscopy at 6 months from the index surgery, and standard surveillance consisting in clinical examination, CEA determination and thoraco-abdominal CT at 6, 12, 24, 36, 48 and 60 months after index surgery.

Inclusion criteria:

• Patients operated (in emergency or elective settings) for colorectal cancer (of the colon, colorectal junction or high rectum).
• Definitive pathological stage pT4 pN0-2 cM0 pMMR and/or pT3-4 pN0-2 cM0 pMMR with positive cytology and/or pT3-4 pN0-2 M1c pMMR with limited peritoneal carcinomatosis which is limited to one abdominal quadrant and was resected during index surgery and no other distant lesion (small indeterminate pulmonary nodules to be followed are accepted)
• Performance status 0-1.
• Age > 18 years.
• Written informed consent.

Exclusion criteria:

• Infraperitoneal rectal cancer (middle or low rectum).
• Age <18 year old.
• Age > 80 year old.
• Hereditary colorectal cancer.
• dMMR/MSI colorectal cancer.
• Inflammatory bowel disease.
• Distant metastasis (outside limited peritoneal carcinomatosis which is limited to one abdominal quadrant and was resected during index surgery and no other distant lesion; small indeterminate pulmonary nodules to be followed are accepted)
• Neo-adjuvant treatment.
• Pregnancy or lactation.
• Immunosuppression.
• Unable to provide informed consent.
• Previous cytoreductive surgery (CRS) (outside limited resection of peritoneal carcinomatosis during index surgery).
• Contraindication to laparoscopy (e.g. severe adhesions, peritonitis).
• Contraindication to and/or no adjuvant chemotherapy.
• History of allergic reaction to oxaliplatin or other platinum-containing compounds.
• Renal impairment, defined as GFR < 50 ml/min, (Cockcroft-Gault equation).
• Myocardial insufficiency, defined as NYHA class > 2.
• Impaired liver function defined as bilirubin ≥ 1.5 x UNL (upper normal limit).
• Inadequate hematological function defined as ANC ≤ 1.5 x 109/l and platelets ≤ 100 x 109/l.