Inclusion Criteria:

1. Patients with resectable or potentially resectable adenocarcinoma of the rectum.

2. Clinical stage by Magnetic Resonance Image (MRI) of pelvis, ultrasonography of liver
and Chest X ray: AJCC T2 N1-2M0 or T3-4 N0-2M0 (patients who require diverting loop
colostomy are eligible). Nuclear medicine study (whole body bone scan or PET scan)
can be performed if clinically indicated.

3. Bi-dimensionally measurable disease by MRI, which can be done with pelvic array coil
and intrarectal tube.

4. Age greater than 18 years and < 80 years, ECOG performance status < 2

5. Biopsy proven adenocarcinoma, superior margin of the tumor below the L5-S1 spine
junction.

6. WBC > 3.5 x109/L, neutrophil count > 1.5x109/L, platelet count > 100x109/L, serum
bilirubin < 1.25xULN (upper limit of normal), AST/ALT < 3x ULN, serum creatinine <
1.25xULN.

7. Informed consent signed.

Exclusion Criteria:

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

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

3. Pregnancy.

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

5. Cardiovascular disease like congestive heart failure, symptomatic coronary artery
disease, or myocardiac infarction.

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

7. Use of aspirin, other NSAID or celecoxib in the two weeks prior to study entry.

8. Patients taking warfarin or other anticoagulating medicine.