Although these data on the effects of daily aspirin are
compelling, it should be acknowledged that these were
secondary analyses of cardiovascular prevention trials not
originally designed to examine cancer incidence or mortality.
Hence, ascertainment of cancer-related endpoints
may be less complete or accurate than would be expected
in a clinical trial with defined cancer outcomes. Some
results were also based upon posttrial follow-up of patients
through linkage with death certificates or cancer registries
and there was no information regarding posttrial usage of
aspirin or nonaspirin nonsteroidal antiinflammatory drugs
(NSAID) or cancer screening. In addition, 2 large randomized
trials of alternate-day aspirin, the Physicians’ Health
Study (PHS) and Women’s Health Study (WHS) did not
show a reduction in CRC incidence (27, 28). The PHS was a
randomized, placebo-controlled trial designed to determine
the effect of aspirin 325 mg/every other day on CV
disease in 22,071 healthy male physicians. The WHS examined
the effect of aspirin 100 mg/every other day on CV
events and overall cancer incidence in 39,876 initially
healthy women. There was no effect of aspirin on the
incidence of CRC over a 10-year follow-up in either trial;
the relative risk of CRC was 1.03 (95% CI, 0.83–1.28) in
the PHS and 0.97 (95% CI, 0.77–1.24) in the WHS (29,
30).