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