An alternative and possibly complementary strategy to
screening is prevention. This can include a variety of lifestyle
and dietary changes or, as is the focus of this review,
aspirin chemoprevention. Several basic science, population-based,
and clinical trials have suggested a protective
effect of aspirin as well as nonaspirin nonsteroidal antiinflammatory
drugs (NSAIDs), including cyclooxygenase-2
(COX-2) inhibitors, against colorectal adenomas and
colorectal cancer. Since age is a major risk factor for colorectal
cancer, with approximately 90% of cases occurring
after age 50 (1), aspirin may be a particularly attractive
intervention; it has documented efficacy in both the primary
and the secondary prevention of cardiovascular disease
(3).
However, aspirin is not risk free; it can increase the
risk for hemorrhagic stroke and gastrointestinal bleeding
(3). Potential harms must be considered in light of the
possibly long period of aspirin exposure used for colorectal
cancer prevention. Furthermore, reductions in colorectal
cancer mortality with chemoprevention would have to be
great enough to compete with the 21% mortality reduction
achieved with simple biannual fecal occult blood testing, or
with the 60% mortality reduction seen with flexible sigmoidoscopy
for lesions within reach of the sigmoidoscope.
Furthermore, data suggest that sigmoidoscopy followed by
colonoscopy when polyps are found could decrease colorectal
cancer incidence by up to 80% (8). The USPSTF
strongly recommends screening of men and women older
than age 50 years (grade A recommendation) (9). A preventive
strategy using aspirin may still have a role as an
adjunct treatment, but the benefits would have to balance
increased risks; in addition, the cost-effectiveness of this
strategy would need to be favorable. Finally, although adherence
to colorectal cancer screening is poor, long-term
adherence to therapy with a chemopreventive agent in otherwise
healthy individuals will probably have a similar
limitation.