Aspirin for Dukes C and High Risk Dukes B Colorectal Cancers

Male or female outpatient of ≥ 18 years of age or ≥ country's legal age for adult consentDukes C colon cancer, high risk Dukes B colon cancer, Dukes B rectal cancer or Dukes C rectal cancer (see Appendix 1 for definition of High Risk Dukes B) Undergone complete resection of primary tumour Completed standard therapy ( at least 3 months of chemotherapy ± radiotherapy ) Within 120 days of completion of standard therapy (surgery, chemotherapy ± radiotherapy) ECOG performance status 0 to 2 Satisfactory haematological or biochemical functions (tests should be carried out within 8 weeks prior to randomisation): Results of clinical investigations carried out within 8 weeks prior to randomisation 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 109/L Platelets ≥ 100 x 109/L Creatinine clearance ≥ 30 mL/min Total bilirubin ≤ 2.0 x the upper limit normal AST & ALT ≤ 5 x the upper limit normal Completed the following investigations Colonoscopy(or CT colonogram(within 16 months prior to randomization) Imaging of abdomen (CT or CT colonogram or MRI or PET or Ultrasound) within 16 months prior to randomization Written informed consent