Radiation Therapy and Either Capecitabine or Fluorouracil With or Without Oxaliplatin Before Surgery in Treating Patients With Resectable Rectal Cancer

Inclusion Criteria: * Patients must consent to participate in the study and must have signed and dated an IRB-approved consent form conforming to federal and institutional guidelines. * Patients must be \> 18 years of age. * Patients must have a life expectancy of 5 years, excluding their diagnosis of cancer (as determined by the investigator), and must have an Eastern Cooperative Oncology Group (ECOG) (Zubrod) performance status of 0 or 1. * Patients must have a diagnosis of adenocarcinoma of the rectum obtained by a biopsy technique which leaves the major portion of the tumor intact. * The interval between the initial diagnosis of rectal adenocarcinoma and randomization must be no more than 42 days. * Prior to randomization, the investigator must specify the intent for sphincter saving or non-sphincter saving surgery. * The tumor must be either palpable by digital rectal exam or be accessible via a proctoscope or sigmoidoscope. * Distal border of the tumor must be located \< 12 cm from the anal verge. * The tumor must be considered by the surgeon to be amenable to curative resection. (Note that curative resection can include pelvic exenteration.) * The tumor must be clinically Stage II (T3-4 N0 with N0 being defined as all imaged lymph nodes are \< 1.0 cm) or Stage III (T1-4 N1-2 with the definition of a clinically positive node being any node \> 1.0 cm). Stage of the primary tumor may be determined by ultrasound or Magnetic Resonance Imaging (MRI). Computed Tomography (CT…