<br>        DISEASE CHARACTERISTICS:<br><br>          -  Histologically confirmed adenocarcinoma of the rectum<br><br>               -  Tumor = 12 cm from the anal verge<br><br>               -  Stage T3-4 or any node-positive disease<br><br>          -  No evidence of metastatic disease (confirmed by negative CT scan of the chest and<br>             abdomen)<br><br>          -  Resectable disease or expected to become resectable after preoperative chemoradiation<br><br>          -  May only be randomized once in this trial<br><br>        PATIENT CHARACTERISTICS:<br><br>          -  WHO/ECOG performance status 0-2<br><br>          -  Hemoglobin = 10.0 g/dL (transfusion allowed to achieve or maintain levels)<br><br>          -  ANC = 1,500/mm^3<br><br>          -  Platelet count = 100,000/mm^3<br><br>          -  ALT and AST = 2.5 times upper level of normal (ULN)<br><br>          -  Alkaline phosphatase = 2.5 times ULN<br><br>          -  Total bilirubin = 1.5 times ULN<br><br>          -  Creatinine clearance > 50 mL/min<br><br>          -  Creatinine = 1.5 times ULN<br><br>          -  Able to swallow tablets<br><br>          -  No prior or concurrent malignancies within the past 5 years except for adequately<br>             treated cone-biopsied carcinoma in situ of the cervix or basal cell carcinoma of the<br>             skin<br><br>          -  No clinically significant (i.e., active) cardiac disease, including any of the<br>             following:<br><br>               -  Congestive heart failure<br><br>               -  Symptomatic coronary artery disease<br><br>               -  Cardiac arrhythmia<br><br>          -  No myocardial infarction within the past 12 months<br><br>          -  No known significant impairment of intestinal resorption (e.g., chronic diarrhea,<br>             inflammatory bowel disease)<br><br>          -  No pre-existing conditions that would preclude chemoradiotherapy or radiotherapy<br>             (i.e., fistulas, severe ulcerative colitis [particularly patients currently taking<br>             sulfasalazine], Crohn's disease, or prior adhesions)<br><br>          -  No peripheral neuropathy = grade 2 by CTCAE v3.0<br><br>          -  No serious uncontrolled intercurrent infections or other serious uncontrolled<br>             concomitant disease<br><br>          -  No history of uncontrolled seizures, central nervous system disorders or psychiatric<br>             disability that, in the opinion of the principal investigator, is clinically<br>             significant and would preclude giving informed consent or interfere with compliance<br>             with oral drug administration<br><br>          -  No psychological, familial, sociological, or geographical condition potentially<br>             hampering compliance with the study protocol and follow-up schedule<br><br>          -  Not pregnant or nursing<br><br>          -  Fertile patients must use effective contraception<br><br>        PRIOR CONCURRENT THERAPY:<br><br>          -  No prior cytotoxic chemotherapy or radiation therapy for rectal cancer<br><br>          -  No prior radiation therapy to the pelvis<br><br>          -  No prior or concurrent investigational drug, agent, or procedure<br><br>          -  More than 4 weeks since prior participation in the active or follow-up period of<br>             another investigational protocol<br><br>          -  No known allergy or any other adverse reaction to any of the study drugs or to any<br>             related compound<br><br>          -  No known dihydropyrimidine dehydrogenase deficiency<br><br>          -  No organ allograft requiring immunosuppressive therapy<br><br>          -  No concurrent sorivudine or chemically related analogues (e.g., brivudine)<br>      ;<br>        DISEASE CHARACTERISTICS:<br><br>          -  Histologically confirmed adenocarcinoma of the rectum<br><br>               -  Tumor = 12 cm from the anal verge<br><br>               -  Stage T3-4 or any node-positive disease<br><br>          -  No evidence of metastatic disease (confirmed by negative CT scan of the chest and<br>             abdomen)<br><br>          -  Resectable disease or expected to become resectable after preoperative chemoradiation<br><br>          -  May only be randomized once in this trial<br><br>        PATIENT CHARACTERISTICS:<br><br>          -  WHO/ECOG performance status 0-2<br><br>          -  Hemoglobin = 10.0 g/dL (transfusion allowed to achieve or maintain levels)<br><br>          -  ANC = 1,500/mm^3<br><br>          -  Platelet count = 100,000/mm^3<br><br>          -  ALT and AST = 2.5 times upper level of normal (ULN)<br><br>          -  Alkaline phosphatase = 2.5 times ULN<br><br>          -  Total bilirubin = 1.5 times ULN<br><br>          -  Creatinine clearance > 50 mL/min<br><br>          -  Creatinine = 1.5 times ULN<br><br>          -  Able to swallow tablets<br><br>          -  No prior or concurrent malignancies within the past 5 years except for adequately<br>             treated cone-biopsied carcinoma in situ of the cervix or basal cell carcinoma of the<br>             skin<br><br>          -  No clinically significant (i.e., active) cardiac disease, including any of the<br>             following:<br><br>               -  Congestive heart failure<br><br>               -  Symptomatic coronary artery disease<br><br>               -  Cardiac arrhythmia<br><br>          -  No myocardial infarction within the past 12 months<br><br>          -  No known significant impairment of intestinal resorption (e.g., chronic diarrhea,<br>             inflammatory bowel disease)<br><br>          -  No pre-existing conditions that would preclude chemoradiotherapy or radiotherapy<br>             (i.e., fistulas, severe ulcerative colitis [particularly patients currently taking<br>             sulfasalazine], Crohn's disease, or prior adhesions)<br><br>          -  No peripheral neuropathy = grade 2 by CTCAE v3.0<br><br>          -  No serious uncontrolled intercurrent infections or other serious uncontrolled<br>             concomitant disease<br><br>          -  No history of uncontrolled seizures, central nervous system disorders or psychiatric<br>             disability that, in the opinion of the principal investigator, is clinically<br>             significant and would preclude giving informed consent or interfere with compliance<br>             with oral drug administration<br><br>          -  No psychological, familial, sociological, or geographical condition potentially<br>             hampering compliance with the study protocol and follow-up schedule<br><br>          -  Not pregnant or nursing<br><br>          -  Fertile patients must use effective contraception<br><br>        PRIOR CONCURRENT THERAPY:<br><br>          -  No prior cytotoxic chemotherapy or radiation therapy for rectal cancer<br><br>          -  No prior radiation therapy to the pelvis<br><br>          -  No prior or concurrent investigational drug, agent, or procedure<br><br>          -  More than 4 weeks since prior participation in the active or follow-up period of<br>             another investigational protocol<br><br>          -  No known allergy or any other adverse reaction to any of the study drugs or to any<br>             related compound<br><br>          -  No known dihydropyrimidine dehydrogenase deficiency<br><br>          -  No organ allograft requiring immunosuppressive therapy<br><br>          -  No concurrent sorivudine or chemically related analogues (e.g., brivudine)<br>