Our results do not have immediate clinical implications.
Confi rmation from randomized trials is necessary before a reduction
in cancer risk could be considered a benefi t of using adultstrength
aspirin. Our results indicate that a randomized trial
examining the effect of aspirin on cancer incidence would need to
be both large and long term, probably lasting a minimum of 10
years. More evidence is needed before any such trial can be justifi ed.
This evidence could come from additional large observational studies
with detailed and prospectively collected information on dose,
frequency, and duration of aspirin use. In addition, if appropriate
biomarkers of breast and prostate carcinogenesis could be identifi
ed, the effect of aspirin on these biomarkers could be tested in relatively
short-term randomized trials, potentially providing further
evidence to justify a long-term randomized trial examining cancer
incidence. Further research to clarify the potential infl uence of
aspirin on cancer risk will be challenging. However, if daily adultstrength
aspirin use is ultimately found to meaningfully reduce
overall cancer risk, there could be important clinical implications
with respect to who should be taking aspirin and at what dose.