DISEASE CHARACTERISTICS:

• Histologically proven previously untreated adenocarcinoma of the rectum that begins within 12 cm of the anal verge by sigmoidoscopy and/or colonoscopy

  • Locally advanced disease defined as any of the following:

    • Fixed or immovable tumor on physical exam
    • T4 disease with invasion of adjacent structures (e.g., pelvic sidewall, sacral pelvis, bladder, or prostate) by CT scan, rectal ultrasound, or MRI
    • T3 disease with invasion through the wall of the muscularis propria by transrectal ultrasound, CT scan, or MRI
• No distant metastatic disease

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• ECOG 0-2

Life expectancy:

• Not specified

Hematopoietic:

• Granulocyte count at least 1,500/mm^3
• Platelet count at least 100,000/mm^3

Hepatic:

• Bilirubin no greater than upper limit of normal (ULN)
• SGOT/SGPT no greater than 2.5 times ULN

Renal:

• Creatinine no greater than 1.5 mg/dL OR
• Creatinine clearance at least 60 mL/min

Other:

• No active second malignancy except nonmelanomatous skin cancer or carcinoma in situ of the cervix
• Patients are not considered to have an active second malignancy if they have completed therapy and are at less than 30% risk of relapse
• No prior or concurrent evidence of neuropathy
• No history of allergy to platinum compounds or antiemetics
• Not pregnant or nursing
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• No prior fluorouracil or platinum-based therapy for any malignancy
• No other concurrent chemotherapy

Endocrine therapy:

• Hormonal therapy allowed only for non-disease related conditions (e.g., insulin for diabetes) OR intermittently as an antiemetic (e.g., dexamethasone)

Radiotherapy:

• No prior pelvic irradiation

Surgery:

• Not specified

Other:

• No concurrent antiretroviral therapy (HAART) for HIV positive patients