Prophylactic PIPAC in Patients With High-risk Colorectal Cancer

• oxaliplatin-based PIPAC (Procedure): Patients operated for pT4 pN0-2 cM0 pMMR colorectal cancer (of the colon, colorectal junction or high rectum) or patients operated for pT3-4 pN0-2 cM0 pMMR colorectal cancer with positive cytology or in patients with pT3-4 pN0-2 M1c pMMR colorectal cancer with limited peritoneal carcinomatosis which is limited to one abdominal quadrant and was resected during index surgery and no other distant lesion, will undergo 6 months of adjuvant systemic chemotherapy associated with 3 cycles of oxaliplatin-based PIPAC (4-6 weeks apart). Each PIPAC session will include exploration laparoscopy (with PCI score), peritoneal lavage for cytology and biopsies of healthy peritoneum of the four quadrants + Douglas + omentum), and oxaliplatin-based PIPAC.
• Control (Standard treatment) (Procedure): Patients operated for pT4 pN0-2 cM0 pMMR colorectal cancer (of the colon, colorectal junction or high rectum) or patients operated for pT3-4 pN0-2 cM0 pMMR colorectal cancer with positive cytology or in patients with pT3-4 pN0-2 M1c pMMR colorectal cancer with limited peritoneal carcinomatosis which is limited to one abdominal quadrant and was resected during index surgery and no other distant lesion, will undergo 6 months of adjuvant systemic chemotherapy, followed by exploration laparoscopy (including 300ml peritoneal lavage for cytology and seven punch peritoneal biopsies in the four quadrants of the abdomen, Douglas and omentum, as well as peritonectomy of 1 cm2) at 6 months after index surgery before entering a standard surveillance program.

Primary outcomes

• 1-year peritoneal metastasis-free survival, [1-year]: The primary endpoint will be the 1-year peritoneal metastasis-free survival, defined as the absence of peritoneal carcinomatosis at 1 year after index surgery, as determined during surveillance. Peritoneal carcinomatosis can diagnosed by any existing modality (as part of a pragmatic approach), including imaging (practiced during surveillance and/or in emergency for ex. for bowel occlusion), surgical exploration (practiced during PIPAC sessions in the intervention group, but also at 6 months after index surgery in the control group, which decrease the risk potential detection bias) and/or pathology. Positive cytology during exploration laparoscopy performed during PIPAC session and/or in the control group will be considered as peritoneal metastasis and therefore as a positive primary outcome.

Secondary outcomes

• 3-year peritoneal metastasis-free survival [3-year]
• Disease-free survival (DFS) [1-year, 3-years]
• Overall survival (OS) [1-year, 3-year]
• 30-day incidence of complications [30-day]
• EORTC QLQ-C30 score 29 [1 month, 2 months, 4 months, 6 months, 12 months, 24 months and 36 months]

Sex: All, ages: 18 Years to any

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.