A Study Comparing Adjuvant Chemotherapy Versus Observation for Patients With Rectal Adenocarcinoma After Neoadjuvant Chemo-Radiotherapy Treatment.

Surgery is the most indicated curative treatment for rectal cancer when disease is diagnosed early, however local recurrence risk increases when the disease is diagnosed at advanced stage.T1-2 tumors have a recurrence rate lower than 10%, while T3N0 tumors have 15% - 35% and positive lymph nodes T3-4 45% to 67% of recurrence rate within 5 years. These data indicate that patient who have a high risk of tumor recurrence should receive an adjuvant therapy treatment. It is possible that adjuvant chemotherapy has a positive impact on survival of patients already treated with neoadjuvant combination therapy. However it is necessary to identify those patients that might have this benefit. An exploratory analysis of the European Organization for Research and Treatment of Cancer (EORTC) 22921 study showed that the addition of adjuvant chemotherapy has benefited only the group of patients who had a reduction of tumor stage to ypT0-2. In the group who had no reduction (ypT3-4), there was no benefit. Retrospective analyzes suggest that the response to neoadjuvant chemoradiotherapy is a predictor of prognosis and even benefit to adjuvant chemotherapy. However the benefit of adjuvant chemotherapy for patients with rectal cancer remains controversial. Therefore, a randomized trial is needed to answer this question. Based on these data the investigators proposed a phase III study, randomized, unblinded, adjuvant chemotherapy based on Fluorouracil(5-FU) and Oxaliplatin versus observation in patients with rectal adenocarcinoma T3-4, N0-1, M0 previously treated with neoadjuvant chemoradiotherapy and who did not presented complete response. The investigator believes that this subgroup of patients, who have not achieved complete response, will be benefit from adjuvant therapy. Study objective: The main objective of this study is verify if adjuvant chemotherapy with 5-FU and oxaliplatin, for 4 months, increases recurrence-free survival versus the observation. Secondary objectives in