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 longterm
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. Cancer Prev Res;
5(2); 164–78. 2011 AACR.