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 diag…