CardioExchange Archive

Although daily aspirin was originally proposed to reduce cardiovascular events, aspirin’s effects on cancer have become increasingly apparent while the vascular benefits, especially in primary prevention, have become less clear. Now a meta-analysis in the Lancet adds important new details to our understanding about the effects of aspirin and increases the evidence in support of a long-term beneficial effect in preventing cancer.

Peter Rothwell and colleagues analyzed data from 51 primary and secondary prevention trials including more than 80,000 patients. They report several key findings

• Daily aspirin reduced deaths from cancer by 15% (p=0·008).
• After 5 years, there was a particularly striking 37% reduction in cancer deaths (p=0·0005), which largely accounted for a reduction in nonvascular deaths overall (p=0·003).
• Aspirin was associated with an initial reduction in major vascular events, but this was offset by increases in major bleeding. With longer follow-up, the vascular effects diminished, so that after 3 years only the reduced risk for cancer was significant.

The authors write that “in view of the very low rates of vascular events in recent and ongoing trials of aspirin in primary prevention, prevention of cancer could become the main justification for aspirin use in this setting…”

In an accompanying comment, Andrew Chan and Nancy Cook point out that the meta-analysis did not include the two largest primary prevention studies, the Women’s Health Study and the Physician’s Health Study, because they used alternate-day aspirin rather than daily aspirin. Both trials failed to find an effect on cancer. Nevertheless, they write, the researchers “show quite convincingly that aspirin seems to reduce cancer incidence and death across different subgroups and cancer sites, with an apparent delayed effect.

“For most individuals, the risk-benefit calculus of aspirin seems to favour aspirin’s long-term anticancer benefit,” they state. However, current evidence does not support “a definitive conclusion about population-based recommendations regarding routine use of aspirin for cancer prevention.” They conclude that in the future, guidelines “can no longer consider the use of aspirin for the prevention of vascular disease in isolation from cancer prevention.”