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

twice daily beginning 5 days prior to radiotherapy and continuing until completion of radiotherapy

Patients receive concurrent fluorouracil IV continuously for 5 weeks.

4-10 weeks after completion of chemoradiotherapy

Patients undergo radiotherapy 5 days a week for 5 weeks

at baseline and then at the time of surgical resection

blood and urine collected 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. specimens are evaluated for COX-2 expression, eicosanoid production, and gene and protein expression using immunohistochemistry, microarray, and mass spectrometry.