Celecoxib, Fluorouracil, and Radiation Therapy in Treating Patients With Stage II or Stage III Rectal Cancer That Can Be Removed By Surgery

OBJECTIVES: * Determine cyclo-oxygenase-2 (COX-2) overexpression in patients with resectable stage II or III rectal cancer treated with neoadjuvant celecoxib, fluorouracil, and radiotherapy. * Determine whether administration of celecoxib, a COX-2 inhibitor, results in changes in tumor (COX-2 overexpressing) levels of eicosanoids but not in the surrounding normal tissue. * Determine if there is a greater change in protein and gene expression in post-treatment biopsies when compared to pretreatment biopsies that are greater for tumor (COX-2 overexpression) than in surrounding normal tissue. * Determine whether patients who express the greatest degree of change in gene and protein expression are those most likely to respond to therapy. * Assess the toxicities of concurrent treatment with celecoxib, fluorouracil, and radiotherapy. OUTLINE: This is a pilot study. Patients receive oral celecoxib twice daily beginning 5 days prior to radiotherapy and continuing until completion of radiotherapy. Patients undergo radiotherapy 5 days a week for 5 weeks. Patients also receive concurrent fluorouracil IV continuously for 5 weeks. Patients undergo radical resection 4-10 weeks after completion of chemoradiotherapy. Patients undergo tumor biopsy at baseline and then at the time of surgical resection. Patients also undergo blood and urine collection at baseline, 5 days after initiation of celecoxib, 7 days after initiation of celecoxib in combination with fluorouracil and radiotherapy, and at the time of surgical resection. The specimens are evaluated for COX-2 expression, eicosanoid production, and gene and protein expression using immunohistochemistry, microarray, and mass spectrometry. After completion of study treatment, patients are followed every 3 months for 2 years, every 6 months for 3 years, and then annually thereafter. PROJECTED ACCRUAL: Approximately 28 patients will be accrued for this study.