OBJECTIVES: I. Determine the maximum tolerated dose and dose-limiting toxicity of postoperative fluorouracil-uracil plus leucovorin calcium concurrently with radiotherapy in patients with colorectal cancer. II. Determine the toxicity of this regimen in these patients. III. Determine the response of tumors in patients with measurable disease treated with this regimen.

OUTLINE: This is a dose-escalation study of fluorouracil-uracil (UFT). Beginning within 10 weeks after definitive surgery, patients receive oral UFT and oral leucovorin calcium (CF) 3 times a day on days 1-28. Treatment continues every 5 weeks for 2 courses in the absence of disease progression or unacceptable toxicity. Beginning on day 1 of the second course, patients undergo radiotherapy to the tumor bed and involved lymph nodes 5 days a week for 5 weeks, followed by boost radiotherapy to the primary tumor bed for 5-16 days. Patients receive 3 additional courses of UFT plus CF beginning 4 weeks after completion of radiotherapy or after recovery from the toxic effects of UFT, whichever occurs later. Patients who have measurable disease with ongoing response after the fifth course receive additional courses of UFT and CF. Cohorts of 3-6 patients receive escalating doses of UFT during the second course until the maximum tolerated dose (MTD) is determined. The MTD is defined as highest dose at which the minority of patients experience dose-limiting toxicity. Patients are followed every 3 months for 1 year and then at the discretion of the investigator.

PROJECTED ACCRUAL: Approximately 30 patients will be accrued for this study.