Inclusion Criteria

Inclusion Criteria

- Male or female outpatient of country's legal age for adult consent

- Dukes C Colon Cancer, High Risk Dukes B Colon Cancer, Dukes B rectal Cancer or Dukes
C Rectal Cancer

- Undergone complete resection of primary tumour

- Completed standard therapy (at least 3 months of chemotherapy +- radiotherapy)

- Within 90 days of completion of standard therapy (Surgery, Chemotherapy +-
radiotherapy)

- ECOG performance status 0-2

- Satisfactory Haematological or biochemical functions (tests should be carried out
within 4 weeks prior to randomization): Results of clinical investigations carried
out within 4 weeks prior to randomization can be used in place of the required
screening investigations. Patients with mild laboratory abnormalities can be included
at the discretion by the site principal investigator, and after approval by ASCOLT
Trial Management Group

- ANC ≥ 1.0 x 10^9/L

- Platelet count ≥ 100 x 10^9/L

- Creatinine clearance > 50 mL/min

- Total bilirubin ≤ 1.5 times upper limit of normal (ULN)

- AST/ALT ≤ 3 times ULN

- Written Informed Consent

Exclusion Criteria

- Familial adenomatour polyposis, inflammatory bowel disease or ulcerative colitis

- Active gastritis or peptic ulcer

- History of continuous daily use of PPI more than 1 year prior to consent

- Gastrointestinal bleeding within the past year

- Hemorrhagic diathesis (i.e., hemophilia)

- Uncontrolled Hypertension (untreated systolic blood pressure > 160 mmHg, or diastolic
blood pressure > 95 mmHg

- History of recent cancers(except for colorectal cancers, non melanoma skin cancers,
basal cell carcinomas, squamous cell carcinomas) in the past 5 years

- History of stroke, coronary arterial disease, angina, or vascular disease

- People who are on current long term treatment with Aspirin, NSAID or Cox-2 inhibitors

- History of erosive GERD or active erosive GERD on gastroscopy

- Patient on antiplatelet agents

- Patient receiving anticoagulants

- Pregnant, lactating, or not using adequate contraception

- Known allergy to NSAIDs or aspirin

- Unexplained rise in CEA (i.e., smoker with elevated CEA will not be excluded)

- Patient on other investigational drug

- Patients with HNPCC (Lynch Syndrome)