Primary prevention of cancer and CVD with aspirin use for over 5 years gives net long-term benefit
Long-term aspirin use lowers the risk of cancer, myocardial infarction (MI) or stroke events. Reduced incidence of CV events with aspirin use has previously been described, but aspirin use is also associated with an age-dependent increased risk of bleeding. Thus, risks and benefits need to be balanced. Evidence was also accumulating that supports a role for aspirin in cancer prevention. To date, no comprehensive data were available on the net benefit of aspirin that could support routine use in the general population. A review of currently available data now published the benefits and harms of prophylactic use of aspirin in the general population, with long-term follow-up.
The results show that aspirin use is associated with a cancer prevention benefit. A reduction in cancer incidence is seen after 3 years of aspirin use, while a minimum of 5 years is needed for mortality reduction. These effects were observed for all daily doses above 75 mg, and no greater benefit was found with increasing doses, in average-risk individuals.
When used as primary prevention, aspirin also reduced serious vascular events in patients at average or low risk (0.51% vs. 0.57% per year), mostly accounted for by a reduction in non-fatal MI. Generally, the CV effect of aspirin was similar in men and women, although the effect of aspirin on coronary heart disease was larger in men and the effect on stroke was larger in women. No reduction was seen in CV mortality in primary prevention trials.
A relative increase of 32-36% in haemorrhagic strokes is reported for aspirin users, from a baseline rate of 0.03% per year. Extracranial bleeds, most of which are gastrointestinal, are more common with 0.7 per 1000 per year, which is increased by about 30-70% with low- or standard-dose aspirin. Rates of gastrointestinal complications and fatality rates show a steep increase in people of 70 years and older, but are generally low below 70 years.
In overall benefit-harm analyses, among individuals taking aspirin for 10 years, the number of men with a cancer, MI or stroke event over a 15-year period, would be (relatively) reduced by 9% and the number of women by 7%. The analyses suggested that a lower cancer incidence accounted for 61-80% of the overall benefit, with a conservative estimate yielding absolute reductions ranging from 0.68% to 3.09%. Major bleeding events would increase by between 0.16% (absolute: 0.21%) and 0.81% (1.05%) from baseline rates of 0.57% to 2.37% over a 15-year period, depending on age and sex. Absolute benefits are greatest in men and at older ages, as they have higher baseline event rates.
While previous analyses on the value of aspirin prophylaxis for CVD benefits in the general population did not show clear benefits, the current analysis of aspirin’s effects on individual cancers, CVD and its harm does suggest favourable benefit-harm profile, with a minimum of 5 years of aspirin use. Longer use probably has greater benefits, but it is uncertain at which age aspirin use should be stopped.
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