Study Evaluating Two Treatment Strategies for Rectal Cancer in Patients ≥75 Years Old

The primary objective of the NACRE-2 trial is to assess whether the addition of chemotherapy after short-course radiotherapy is more effective than short-course radiotherapy alone in elderly patients with locally advanced rectal cancer. Secondary objectives will assess the efficacy and safety profile of the combination, as well as its effect on patients' quality of life. Patients will be separated into two groups to receive their assigned treatment: * Group 1: Short-duration radiotherapy according to standard practice lasting one week, followed by chemotherapy with FOLFOX4s consisting of oxaliplatin (85 mg/m²), folinic acid (400 mg/m²) and 5-Fluoro-Uracil (400 mg/m² administered in hospital, followed by 2400 mg/m² administered over 46 hours at home) every two weeks for 3 months * Group 2: Short-duration radiotherapy according to standard practice, lasting one week To receive treatment, patients must come to the hospital where, at each visit, the medical team will carry out medical examinations, prior to administering treatment, to assess the patient's general state of health and tolerance to treatment. A radiological assessment of the disease will be carried out 11 weeks after the end of radiotherapy. Patients whose tumors have not shrunk will undergo surgery to remove them and enter the follow-up phase. Patients whose tumors have shrunk will not undergo surgery, and will enter a surveillance phase. At 21 weeks, patients whose tumors are still present will undergo surgery and enter the follow-up phase. Patients whose tumors have disappeared will remain in a surveillance phase. During the surveillance or follow-up phases, patients will be monitored in hospital every 3 months (if no progression is observed). In the case of surgery, patients will be monitored every 6 months. The maximum duration of treatment is 3 years.