Standard treatment for locally advanced cancer of the rectum is preoperative chemoradiotherapy with 5-Fluorouracil (5-FU) plus 4 cycles of postoperative chemotherapy with 5-FU. According to our previous study (CAO/ARO/AIO-94, published in the New England Journal of Medicine 2004; 351:1731-40) this treatment results in only 6% of local failures, yet, still 36% of all patients develop distant metastasis. Therefore, our new study (CAO/ARO/AIO-04) incorporates new drugs, i.e. 5-FU + oxaliplatin, in an effort to improve the control of distant metastases. It is our hypothesis that the rate of disease free survival will improve by 5 to 8% after 3 years of follow-up.

Inclusion Criteria:

• Minimum age: 18 years
• Histologically proven, advanced primary carcinoma of the rectum (tumor ? 12cm from the anal verge, with clinically staged T3/4 or any node-positive disease
• No prior therapy except a diverting stoma
• ECOG PS less than or equal 2
• Adequate bone marrow function: Leukocytes > 3,5 x 10^9/L Absolute neutrophil count > 1,5 x 10^9/L Platelet count > 100 x 10^9/L Hemoglobin > 10 g/dl
• Adequate hepatic function: Total bilirubin < 2,0 mg/dl ALAT, ASAT, alkaline phosphatase, gamma-GT < 3 x ULN 7. Serum creatinine < 1,5 mg/dl, creatinine-clearance > 50 ml/min
• Written informed consent before randomization

Exclusion Criteria:

• Pregnant or breast feeding women
• Fertile patients without adequate contraception during therapy
• Past or ongoing drug abuse or alcoholic excess
• Prior chemotherapy
• Prior radiotherapy to the pelvis
• Prior (within 4 weeks) or concurrent treatment with any other investigational agent
• Psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule
• History of severe somatic or psychological diseases: - instable cardiac disease not well controlled with medication, myocardial infarction within the last 6 months:* Central nervous system disorders or psychiatric disability including dementia or epileptic disease; * active uncontrolled intercurrent infections or sepsis
• Peripheral neuropathy > 2 (NCI CTC AE grading)
• Previous or concurrent malignancies, with the exception of adequately treated basal cell carcinoma of the skin or in situ carcinoma of the cervix. The inclusion of patients with other adequately treated tumors within the last 5 years has to be discussed with the principal investigator
• Chronic diarrhea (> NCI CTC AE-Grad 1)
• Known allergy to substances containing platinum compounds
• Concurrent use of the antiviral agent sorivudine or chemically related analogues
• Known deficiency of dehydropyrimidindehydrogenase (DPD)