Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histopathologically confirmed rectal adenocarcinoma meeting the following criteria:

- Inferior aspect of tumor is > 4 cm from anal verge on digital examination and
pelvic MRI scan

- Superior aspect of tumor is not higher than the anterior aspect of the S1/S2
interspace on pelvic MRI scan

- Mesorectal fascia is not threatened or involved (tumor > 1 mm from mesorectal
fascia)

- Primary tumor meets 1 of the following criteria:

- T3a-b (mesorectal primary tumor invasion seen ≤ 5 mm beyond muscularis
propria) in the presence of 1 of the following:

- Extra-mural vascular invasion

- Mesorectal lymph node(s)/tumor deposit(s) with irregular border and
mixed signal intensity

- Any T3c (primary tumor invasion seen > 5 mm beyond muscularis propria)-T4a
(invasion of visceral peritoneum for tumors with a component above
peritoneal reflection)

- Low tumors should not involve levator ani (> 1 mm gap between tumor and levator
ani) or anal sphincters

- No evidence of distant metastases or stage T4b cancer with invasion into adjacent
organs or structures

- Must have measurable disease at the baseline visit

- Impending rectal obstruction is permitted if relieved by a non-functioning ileostomy
or colostomy

- No disease threatening mesorectal fascia (disease ≤ 1 mm from mesorectal fascia
whether this is primary tumor, extra-mural vascular invasion, or tumor deposit with
irregular border and mixed signal intensity)

PATIENT CHARACTERISTICS:

- ECOG performance status 0-1

- Hemoglobin ≥ 9 g/dL

- WBC ≥ 3 x 10^9/L

- Absolute neutrophil count ≥ 1.5 x10^9/L

- Platelet count ≥ 100 x10^9/L

- Total bilirubin ≤ 1.5 times upper limit of normal (ULN)

- Alkaline phosphatase ≤ 5 x ULN

- AST or ALT ≤ 2.5 x ULN

- Creatinine clearance ≥ 50 mL/min

- Magnesium and calcium normal

- Candidate for systemic therapy, in the opinion of the primary oncologist

- No known significant impairment of intestinal absorption (e.g., chronic diarrhea,
inflammatory bowel disease)

- No evidence of established or acute ischemic heart disease (e.g., left bundle branch
block, pathological q-waves, ST elevation, or ST-segment depression) and normal
clinical cardiovascular assessment by ECG

- No enlarged pelvic sidewall lymph nodes

- No severe local bowel symptoms of tenesmus or irregularity or frequency of bowel
habit precluding accurate assessment of diarrhea

- No pelvic sepsis

- No uncontrolled infection

- Not pregnant or nursing

- Fertile patients must use effective contraception during treatment and for 6 months
after completion of treatment

- No other prior or current malignant disease that, in the judgement of the treating
investigator, is likely to interfere with study treatment or assessment of response

- No clinically significant cardiovascular disease, including any of the following
within the past year:

- Myocardial infarction

- Unstable angina

- Symptomatic congestive heart failure

- Serious uncontrolled cardiac arrhythmia

- No history of interstitial lung disease (e.g., pneumonitis or pulmonary fibrosis or
evidence of interstitial lung disease)

PRIOR CONCURRENT THERAPY:

- No prior pelvic radiotherapy

- No metallic colon stent or rectal stent in situ

- More than 30 days since prior chemotherapy, radiotherapy, hormonal treatment,
antibody therapy, immunotherapy, gene therapy, vaccine therapy, angiogenesis
inhibitors, matrix metalloproteinase inhibitors, thalidomide, anti-VEGF/Flk-1
monoclonal antibodies, or other experimental drugs