Considerable evidence supports the effectiveness of
aspirin for
chemoprevention of
colorectal cancer (CRC) in addition to its well-established benefits in the prevention of
vascular disease. Epidemiologic studies have consistently observed an inverse association between
aspirin use and risk of CRC. A recent pooled analysis of a long-term posttrial follow-up of nearly 14,000 patients from four randomized,
cardiovascular disease prevention trials showed that daily
aspirin treatment for about five years was associated with a 34% reduction in 20-year CRC mortality. A separate metaanalysis of nearly 3,000 patients with a history of colorectal
adenoma or
cancer in four randomized
adenoma prevention trials showed that
aspirin reduced the occurrence of advanced
adenomas by 28% and any
adenoma by 17%.
Aspirin has also been shown to be beneficial in a clinical trial of patients with
Lynch syndrome, a hereditary CRC syndrome; in those treated with
aspirin for at least two years, there was a 50% or more reduction in the risk of CRC commencing five years after randomization and after
aspirin had been discontinued. A few observational studies have shown an increase in survival among patients with CRC who use
aspirin. Taken together, these findings strengthen the case for consideration of long-term
aspirin use in CRC prevention. Despite these compelling data, there is a lack of consensus about the balance of risks and benefits associated with long-term
aspirin use, particularly in low-risk populations. The optimal dose to use for
cancer prevention and the precise mechanism underlying
aspirin's anticancer effect require further investigation.