The Lancet has published the results of a meta-analysis that aimed to assess the effects of daily aspirin on cancer incidence, mortality, and non-vascular death. The results of this study have been widely reported in the media (BBC).
This analysis included data from 51 studies involving 77,549 patients. 40,269 were assigned to treatment with aspirin and 37,280 to a control. Trials were included if treatment allocation was random and included an intervention of daily aspirin with a follow up of at least 90 days. The trials were designed to assess cardiovascular outcomes included both primary and secondary prevention of events. The dose of aspirin use varied.
The data were analysed for vascular and non-vascular deaths and cancer death data was accessed at individual patient level where this was possible, otherwise it was extracted from the original trial report or subsequent publications.
Aspirin was reported to reduced cancer deaths (OR 0·85, 95% CI 0·76–0·96, p=0·008) in a dataset involving 34 trials. This became more apparent after 5 years of follow up and onwards (OR 0·63, 95% CI 0·49–0·82, p=0·0005).
In an analysis of primary prevention trials using low dose aspirin cancer risk was reduced from 3 years onwards (OR 0·76, 95% CI 0·66–0·88, p=0·0003) and this effect was present in men and women. It was noted that benefits in reduction of cardiovascular events were offset by an increased risk of major bleeds initially but that over time both of these effects diminished while the cancer benefit appeared to remain.
An analysis to examine consistency across gender, age and smoking status found that the absolute risk reduction is approximately 3 cases per 1000 patient-years across all groups but only after a minimum of three years of treatment.
This analysis does have some limitations. The Women's Health Study was excluded from the analysis as the aspirin was dosed on alternate days; it has not shown a reduction in cancer incidence. The trials were not designed to examine cancer outcomes and in some cases the data for non-fatal cancers was patient reported although this was usually supported by a review of medical records.
The authors conclude that, "prevention of cancer could become the main justification for aspirin" but also note that "more research is required to identify which individuals are likely to benefit most".
An accompanying editorial notes that data are awaited for additional trials. Longer term follow up from the Women's Health Study and Physicians’ Health Study is also awaited, especially as these two studies have not shown a cancer benefit after 10 to 12 years of alternate day dosing of aspirin.
Action: Clinicians should be aware of this recent study and its broad media coverage. The absolute benefit is small; it may be wise to await national guidance before recommending aspirin for use in this way.