Inclusion Criteria:

- patients with resectable or potentially resectable adenocarcinoma of the rectum

- clinical stage T2 N1-2 or T3-4 N0-2 (patients who require diverting loop colostomy
are eligible)

- age greater than 18 years, ECOG performance status < 2 (appendix, section 13.1)

- biopsy proven adenocarcinoma, superior margin of the tumour within 15cm of the anal
verge on rigid sigmoidoscopy

Exclusion Criteria:

- Distant metastasis, Prior pelvic irradiation, Inflammatory bowel disease, Medical
conditions which preclude radical therapy

- History of malignancy within five years (except nonmelanoma skin cancer, CIN cervix)

- Pregnancy

- Hypersensitivity to celecoxib, NSAID, sulfonamides or 5-FU

- Significant comorbid illness

- History of peptic ulcer disease or NSAID-related gastrointestinal bleeding

- Use of aspirin, other NSAID or coxib in the two weeks prior to study entry

- Neutrophil count <1.5x109/L, platelet count <100x109/L, serum bilirubin >1.25xULN
(upper limit of normal), AST/ALT >3xULN, serum creatinine >1.25xULN