DISEASE CHARACTERISTICS:

* Biopsy-proven primary adenocarcinoma of the rectum

* Stage II or III disease
* The distal border of the tumor must be at or below the peritoneal reflection, defined as within 12 cm of the anal verge by proctoscopic examination
* No recurrent disease
* Must have wild-type k-ras status
* Measurable and/or nonmeasurable disease

PATIENT CHARACTERISTICS:

* Zubrod performance status 0-2
* Leukocyte count ≥ 3,000/mcL
* Granulocyte count ≥ 1,500/mcL
* Platelet count ≥ 100,000/mcL
* Bilirubin ≤ 1.5 times upper limit of normal (ULN)
* Alkaline phosphatase ≤ 2.5 times ULN
* SGOT (serum glutamate oxaloacetate transaminase) or SGPT (serum glutamate pyruvate transaminase)≤ 2.5 times ULN
* Creatinine clearance \> 50 mL/min
* No prior severe reaction to a monoclonal antibody
* Willing to have specimens submitted
* No peripheral neuropathy ≥ grade 2
* No known existing uncontrolled coagulopathy
* No evidence of current high-grade obstruction

* At least 2 weeks since prior diverting procedure
* No history of allergy to platinum compounds or to antiemetics appropriate for administration in conjunction with protocol treatment
* No prior unanticipated severe reaction to fluoropyrimidine therapy or known sensitivity to fluorouracil or known DPD deficiency
* No active inflammatory bowel disease, malabsorption syndrome, or inability to swallow that would impair the ingestion or absorption of capecitabine
* No uncontrolled intercurrent illness
* No ongoing or active infection
* No symptomatic congestive heart failure or unstable angina pectoris
* No cardiac arrhythmia or myocardial infarction within the past 12 months
* Not pregnant or nursing
* Fertile patients must use effective contraception
* No prior malignancy allowed except for adequately treated basal cell or squamous cell skin cancer, carcinoma in situ of the cervix, or other cancer from which the patient has been disease-free for 5 years

PRIOR CONCURRENT THERAPY:

* Recovered from any recent major surgeries (e.g., coronary artery bypass graft, transurethral resection of prostate, or abdominal surgery)
* No prior chemotherapy, radiotherapy, or targeted therapy for this tumor
* More than 4 weeks since prior investigational agents
* No concurrent anti-retroviral therapy for HIV