Neoadjuvant Chemotherapy for Obstructive Colon cancER First Treated by cOlostomy

Inclusion Criteria: * Age ≥ 18 years * ECOG performance status 0 or 1 * Patients with obstructive colon cancer treated by defunctioning stoma * Pathologically confirmed adenocarcinoma (≥10 cm from the anal verge- left transverse colon) - MSS/pMMR (microsatellites stable primary tumor) status * Patient requiring colectomy * Laboratory data including : White blood cell count ≥ 3.109 /L with Neutrophils ≥ 1,5.109 / L, Platelet count ≥ 100.109 / L, Hemoglobin ≥ 9 g/dL (5,6 mmol/L), Total bilirubin ≤ 1,5 x ULN (upper limit of normal), ASAT and ALAT ≤ 2,5 x ULN, Alkaline phosphatase ≤ 1,5 x ULN, Serum creatinine ≤ 1,5 x ULN (performed 10-15 days prior to randomization). * Non metastatic colon cancer (lung, liver, peritoneal) on thoracic-abdomino-pelvis CT scan * Absence of synchronous colorectal cancer * No prior chemotherapy or abdominal or pelvic irradiation * No history of colorectal cancer * No serious medical co-morbidity : uncontrolled inflammatory bowel disease, uncontrolled angina, recent \[within the past 6 months\] myocardial infarction, or another serious medical condition, judged to compromise ability to tolerate chemotherapy and/or surgery * Women of childbearing potential with effective contraception will be required during chemotherapy treatment and for 6 months after cessation of chemotherapy treatment and a negative blood pregnancy test by beta-HCG at inclusion. * Women surgically sterile (absence of ovaries and/or uterus) * Postmenopausal women: confirmation diagnostic (non-medically induced amenorrhea for at least 12 months prior to the inclusion visit) * For men participating in the study, contraception is required during the trial and for 6 months after stopping chemotherapy treatment. * Patient able to comply with the study protocol, in the investigator's judgment * Patient affiliated with, or beneficiary of a social security (national health insurance) category * Person informed and having signed his consent Exclusion Criteria: * Contraindication to colectomy and/or anesthesia * Rectal cancer located within 10 cm of the anal verge by endoscopy or under the peritoneal reflection at surgery * Patient having received radiation therapy prior to surgery * Metastatic spread at baseline assessment (lung, liver, peritoneal) * History or current evidence on physical examination of central nervous system disease or; Peripheral neuropathy ≥ grade 1 * Contraindication to study neoadjuvant chemotherapy treatments * Presence of inflammatory bowel disease, HNPCC syndrome or polyposis Clinically relevant coronary artery disease or history of myocardial infarction in the last 6 months, or high risk of uncontrolled arrhythmia * Uracilemia ≥ 150 ng/ml (suggestive of complete DPD deficiency) * Medical, geographical, sociological, psychological or legal conditions that would not permit the patient to complete the study or sign informed consent * Any significant disease, which, in the investigator's opinion, would exclude the patient from the study. * Patient is a pregnant (positive blood pregnancy test) or breastfeeding (lactating) woman or intending to become pregnant during the study and for at least 6 months after the treatment termination * Person deprived of liberty by administrative or judicial decision or placed under judicial protection (guardianship or supervision) * Simultaneous participation in another interventional research