Inclusion Criteria:

- Biopsy proven adenocarcinoma of the rectum

- Lesion evaluated by surgeon and found to be resectable

- Stage T3 or T4 disease on radiography or ultrasound

- 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

- Informed consent signed

- 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 prior malignancy in the past 5 years except: skin cancer or in-situ
cervical cancer. However, patients with synchronous adenocarcinomas are eligible
provided either (a) the synchronous adenocarcinoma was in a removed pedunculated
polyp and did not invade the stalk or (b) the synchronous adenocarcinoma was in a
removed polyp that lay within the surgical field (extent of resection would not be
changed) or (c) the synchronous adenocarcinoma is smaller than the index rectal
cancer and lies completely within the radiation field (clinically favorable second
lesion and the extend of radiation and surgery would not be changed).

- Patients with known allergy to 5-fluorouracil or irinotecan