Evidence from a wide range of sources suggests that individuals taking aspirin and related non-steroidal
anti-infl ammatory drugs have reduced risk of large bowel cancer. Work in animals supports cancer reduction with
aspirin, but no long-term randomised clinical trials exist in human beings, and randomisation would be ethically
unacceptable because vascular protection would have to be denied to a proportion of the participants. However,
opportunistic trials of aspirin, designed to test vascular protection, provide some evidence of a reduction in cancer,
but only after at least 10 years. We summarise evidence for the potential benefi t of aspirin and natural salicylates in
cancer prevention. Possible mechanisms of action and directions for further work are discussed, and implications for
clinical practice are considered.