• 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