ASCOLT Aspirin for Dukes C and High Risk Dukes B Colorectal Cancers.

Interventions: Eligible participants will be randomised to the study in 1:1 ration to either Aspirin arm: 200 mg Aspirin (oral tablet) once a day for 3 years or Placebo equivalent.
The study treatment is given as adjuvant therapy
Drug compliance will be monitored via drug dispensations and drug returns, recorded on drug accountability logs at each study visit.
Noncompliance is defined as omission of more than 30% of the study period that the patient is on the study.
Primary outcome(s): Disease Free Survival (DFS) among all eligible subjects (high risk Dukes B colon cancer, Dukes C colon cancer and rectal cancer patient sub-groups)
[During treatment: prior to each treatment cycle. Patient will have 3 monthly assessments for 3 years (month 3 to month 36) followed by 6 monthly assessments for additional 2 years (month 42 to month 60).]
Study Design: Purpose: Treatment; Allocation: Randomised controlled trial; Masking: Blinded (masking used);Assignment: Parallel;Type of endpoint: Safety/efficacy