Inclusion Criteria:

- Histologically confirmed rectal carcinoma

- Primary tumor evaluated by pelvic MR Imaging:

i) iT3 ≥c tumors, with MRI showing a predictive CRM ≤ 2 mm or a EMS (Extra Mural
Spread) ≥ 5 mm

ii) Resectable iT4 tumors (only randomized within the "poor responders" group)

iii) Any T tumors with MRI showing a predictive CRM ≤ 1 mm

- No detectable metastases: Thorax-abdomen-pelvic CT-scan

- Patient ≥ 18 years

- ECOG Performance Status 0-1-2

- Patient information and written informed consent form signed

- Patient who can receive radiotherapy and chemotherapy

- Negative pregnancy test in women of childbearing potential

- Patient covered by a Social Security system

- Hematology : Haemoglobin ≥ 9 g/dL, WBC ≥ 4000/mm3, neutrophils ≥ 1.5 x 109/L,
platelets ≥ 100 x 109/L

- Hepatic function : total bilirubin ≤ 1.5 x ULN, AST and ALT ≤ 3 x ULN, Alkaline
phosphatases ≤ 3 x ULN

- Renal function : creatinine ≤ 1.25 x ULN or creatinine clearance ≥ 60 ml/min

Exclusion Criteria:

- Indication for immediate surgery

- Primary tumor not measured at the MRI before inclusion

- Previous pelvic radiotherapy

- Contraindication to radiotherapy and/or chemotherapy

- Severe renal or liver impairment

- Cardiac and/or coronary disease which could contraindicate 5-Fu administration

- Active infectious disease

- Peripheral sensitive neuropathy

- History of prior cancer (except if it was cured more than 5 years ago, and if
complete remission)

- Patient (male or female) of reproductive potential not using an effective
contraceptive method during the whole treatment and up to 6 months after the
completion of treatment

- Concurrent participation in any other clinical trial likely to interfere with the
therapeutic schedule

- Fertile female patient not using adequate contraception, or breast-feeding woman