The DUREC trial comprises three treatment periods: induction chemotherapy, chemoradiotherapy and waiting period until surgery.

Durvalumab (MEDI4736) will be supplied in glass vials containing 500 mg of liquid solution at a concentration of 50 mg/mL for intravenous(IV) administration. Flat dose of 1500 mg every 4 weeks will be administered during induction chemotherapy, chemoradiotherapy and waiting period until surgery.

Induction chemotherapy (Week 1-12) Patients will be treated with Durvalumab and FOLFOX6 regimen. Modified FOLFOX6 regimen consists of 2-hour infusion of oxaliplatin (85 mg/m2) and 2-hour infusion of leucovorin (400 mg/m2) on Day l, followed by 5-fluorouracil (5-FU) bolus (400 mg/m2) on Day 1 and 44-hour on continuous infusion (2400 mg/m2). FOLFOX6 regimen will be repeated at 2-week intervals.

Chemoradiotherapy (Week 13-20) Patients will be treated with Durvalumab, radiotherapy and capecitabine. All patients will receive 28 daily (5/7 days) fractions of 1.8 Gy up to a total dose of 50.4 Gy to the pelvic field including the tumour bed with a margin and the regional lymph nodes.

Capecitabine will be given during radiotherapy in a dose of 825 mg/m2 bid (twice per day) 7/7 days during all radiotherapy period (38 days approximately, considering bank holidays and radiotherapy machinery periodic revisions) Waiting period until surgery (21-31) Patients will be treated with Durvalumab on week 21 and 25. To assess the tolerability and toxicity profile of the combination of mFOLFOX6 + durvalumab and CRT + durvalumab the investigators plan to perform a run-in treatment phase including the first 6 patients in the study and stop recruitment until the last of these 6 patients will be operated and 30-days postsurgery period will be completed. If 2 or less dose limiting toxicities (DLTs) related with durvalumab therapy are observed in these 6 patients, recruitment will be opened again to reach the planned 58 patients.