Inclusion Criteria:

- Patients must have an Eastern Cooperative Oncology Group (ECOG) Status of 0 or 1, or
comparable Karnofsky performance status

- Patients must have histologically confirmed invasive adenocarcinoma of the rectum
Distal border of the tumor must be within 12 cm from the anal verge as measured on
rigid proctoscopic exam

- Patients must have Stage II (uT3-4, uN0) or Stage III (any T, uN1-2) tumors, as
confirmed by ERUS or MRI; females with anterior tumors invading the posterior vaginal
wall (uT4) and males with anterior tumors that invade the seminal vesicles or
adjacent organs (uT4) will also be eligible provided they undergo an extended
resection including the organs involved

- Patients with high grade obstruction that impedes the ERUS exam are eligible for the
study provided they can be staged by MRI

- Patients with synchronous or metachronous colorectal cancer are eligible for the
study on condition that they are treated for rectal cancer in accordance with the
protocol

- Patients with the following are NOT allowed on study:

- Metastatic disease or other primaries

- Locally recurrent rectal cancer

- Previously documented history of Familial Adenomatous Polyposis

- History of Inflammatory Bowel Disease

- History of prior radiation treatments to pelvis

- History of clinically significant cardiac disease (i.e., Class 3-4 congestive
heart failure, symptomatic coronary artery disease, uncontrolled arrhythmia,
and/or myocardial infarction within the previous 6 months

- History of uncontrolled seizures or clinically significant central nervous
system disorders

- History of psychiatric conditions or diminished capacity that could compromise
the giving of informed consent, or interfere with study compliance

- History of allergy and/or hypersensitivity to 5-fluorouracil (fluorouracil),
leucovorin (leucovorin calcium), and/or oxaliplatin

- History of difficulty or inability to take or absorb oral medications

- Patients must have adequate bone marrow, hepatic and renal function within 7 days
prior to registration

- White blood cells (WBC) >= 3,000 mm^3

- Absolute neutrophil count (ANC) > 1,500 mm^3

- Hemoglobin > 9.5 mg/dl

- Platelet count >= 100,000 mm^3

- Total bilirubin =< 1.5 mg/dl

- Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase [SGOT]) =<
2.0 times institutional upper limit of normal (ULN)

- Alanine aminotransferase (ALT) (serum glutamic pyruvic transaminase [SGPT]) =< 2.0
times ULN

- Alkaline phosphatase =< 2.0 times ULN

- Serum creatinine =< 1.5 times ULN

- Patients with hereditary non-polyposis colorectal cancer are eligible for the study
provided they meet the rest of the eligibility criteria

- Patients who have experienced a prior malignancy should have received potentially
curative therapy for that malignancy, and should be cancer-free for at least five
years from the date of initial diagnosis (Exceptions: patients treated for basal cell
carcinoma, or carcinoma in-situ of the cervix)

- Patients of reproductive potential should agree to use an effective method of birth
control when undergoing treatments with known or possible mutagenic or teratogenic
effects; all female participants of childbearing potential must have a negative urine
or serum pregnancy test within two weeks prior to study registration

- Patients or the patient's legally acceptable representative must provide written
authorization to allow the use and disclosure of protected health information; NOTE:
this may be obtained in either the study-specific informed consent or in a separate
authorization form and must be obtained from the patient prior to study registration
or the initiation of any study-specific procedures