Five Fractions of Radiotherapy Followed by Full Dose FOLFOX Chemotherapy as Preoperative Treatment for Rectal Cancer

Inclusion Criteria: * Biopsy proven adenocarcinoma of the rectum * Patient evaluated by surgeon and found to be a potential surgical candidate. Since the primary objectives are response to chemoradiation and acute toxicity, lesions which are initially unresectable are eligible-provided the surgeon feels that, if there is sufficient response, surgery could become feasible. * Clinical evidence of T3 or T4 disease. This can be by imaging studies (see or by physical findings (tethering on palpation for T3 lesions or invasion of a neighboring organ for T4 lesions) * Karnofsky Performance Status at \>60 * Laboratory criteria: * Absolute neutrophil count \>= 1.5 K * Platelets \>= 100 K * Total Bilirubin \<= 2.0; * SGOT and Alkaline Phosphatase \<= 2 x upper limit of normal * Creatinine \< 2.0 * Hemoglobin \>= 8.0 * Informed consent signed * Tumor measurable in at least one dimension. This may be, e.g. length and/or width measured endoscopically or on digital rectal examination, and maximum rectal wall thickness determined by imaging studies. * Estimated longevity at least 12 months * Patients with distant metastatic disease will be eligible if they satisfy all other conditions Exclusion Criteria: * Pregnant women, children \< 18 years, or patients unable to give informed consent * Patients with a past history of pelvic radiotherapy. * Patients with any other malignancy within the past 5 years except: skin cancer or in-situ cervical cancer * Patients with known allergy/intolerance to 5FU, Leucovorin, Oxaliplatin, Capecitabine * Prior chemotherapy for colorectal cancer. * Grade \>= 2 peripheral neuropathy * Any condition which, in the opinion of the treating medical oncologist, renders the patient unfit for 5FU (oral capecitabine if 5FU is unavailable), Leucovorin, Oxaliplatin chemotherapy