Radiation Therapy, Surgery, and Chemotherapy in Treating Patients With Rectal Cancer That Can Be Surgically Removed

OBJECTIVES: * Compare the disease-free and overall survival in patients with resectable adenocarcinoma of the rectum treated with preoperative radiotherapy with or without preoperative fluorouracil (5-FU) combined with leucovorin calcium (CF) and/or postoperative 5-FU/CF. OUTLINE: This is a randomized, multicenter study. Patients are stratified according to center, sex, tumor location (0-5 vs 6-10 vs 11-15 cm from anal margin), and stage (T3 vs T4). Patients are randomized to 1 of 4 treatment arms. * Arm I: Patients undergo involved-field radiotherapy 5 days a week for 5 weeks followed 3-10 weeks later by abdominoperineal resection or anal-sparing resection according to local practice in the absence of disease progression or unacceptable toxicity. * Arm II: Patients undergo radiotherapy as in arm I beginning on day 1 and leucovorin calcium (CF) IV followed by fluorouracil (5-FU) IV (1 hour before radiotherapy) on days 1-5 and 29-33, followed 3-10 weeks later by resection as in arm I in the absence of disease progression or unacceptable toxicity. * Arm III: Patients undergo radiotherapy followed 3-10 weeks later by resection as in arm I. Within 3-10 weeks after resection, patients receive CF followed by 5-FU on days 1-5. Chemotherapy continues every 4 weeks for 4 courses in the absence of disease progression or unacceptable toxicity. * Arm IV: Patients undergo preoperative radiotherapy with concurrent chemotherapy followed by resection as in arm II and postoperative chemotherapy as in arm III. Patients are followed every 6 months. PROJECTED ACCRUAL: A total of 992 patients will be accrued for this study within 4 years.