A series of remarkable clinical, epidemiological, and laboratory studies has shown that aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) such as sulindac, can prevent the development of colorectal cancer and cause regression of pre-existing adenomas.1 Aspirin is one of the most potent chemopreventive agents against colorectal cancer. However, its mechanism for causing a reduction in colorectal cancer risk and mortality is unknown.2 The anti-inflammatory properties of NSAIDs are thought to reside in their ability to inhibit prostaglandin production at sites of inflammation.

Cyclooxygenase (COX) is a key enzyme in the production of prostaglandins, and aspirin can inhibit its activity directly. Initially, COX was thought to be a single enzyme, but in 1991 a second COX isoform was discovered (COX-2) which is induced by cytokines, growth factors, and tumour promoters.3 COX-1 is expressed constitutively in many …