Limited Benefit Of Aspirin For Prevention Of Cardiovascular Events And Cancer

Queequeg

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Sep 15, 2016
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I am not sure if this came up before as I couldn't find a discussion on it but I am wondering what you guys think about this Meta Review of the available research on aspirin. I know risk of internal bleeding is typically overstated but they also show limited benefit with respect to CVD and cancer.

Aspirin in Primary Prevention of Cardiovascular Disease and Cancer: A Systematic Review of the Balance of Evidence from Reviews of Randomized Trials

Aspirin in primary prevention of cardiovascular disease and cancer: a systematic review of the balance of evidence from reviews of randomized trials.

Abstract
BACKGROUND:
Aspirin has been recommended for primary prevention of cardiovascular disease (CVD) and cancer, but overall benefits are unclear. We aimed to use novel methods to re-evaluate the balance of benefits and harms of aspirin using evidence from randomised controlled trials, systematic reviews and meta-analyses.

METHODS AND FINDINGS:
Data sources included ten electronic bibliographic databases, contact with experts, and scrutiny of reference lists of included studies. Searches were undertaken in September 2012 and restricted to publications since 2008. Of 2,572 potentially relevant papers 27 met the inclusion criteria. Meta-analysis of control arms to estimate event rates, modelling of all-cause mortality and L'Abbé plots to estimate heterogeneity were undertaken. Absolute benefits and harms were low: 60-84 major CVD events and 34-36 colorectal cancer deaths per 100,000 person-years were averted, whereas 46-49 major bleeds and 68-117 gastrointestinal bleeds were incurred. Reductions in all-cause mortality were minor and uncertain (Hazard Ratio 0.96; 95% CI: 0.90-1.02 at 20 years, Relative Risk [RR] 0.94, 95% CI: 0.88-1.00 at 8 years); there was a non-significant change in total CVD (RR 0.85, 95% CI: 0.69-1.06) and change in total cancer mortality ranged from 0.76 (95% CI: 0.66-0.88) to 0.93 (95% CI: 0.84-1.03) depending on follow-up time and studies included. Risks were increased by 37% for gastrointestinal bleeds (RR 1.37, 95% CI: 1.15-1.62), 54%-66% for major bleeds (Rate Ratio from IPD analysis 1.54, 95% CI: 1.30-1.82, and RR 1.62, 95% CI: 1.31-2.00), and 32%-38% for haemorrhagic stroke (Rate Ratio from IPD analysis 1.32; 95% CI: 1.00-1.74; RR 1.38; 95% CI: 1.01-1.82).

CONCLUSIONS:
Findings indicate small absolute effects of aspirin relative to the burden of these diseases. When aspirin is used for primary prevention of CVD the absolute harms exceed the benefits. Estimates of cancer benefit rely on selective retrospective re-analysis of RCTs and more information is needed.

This meta study also claims a limited benefit for CVD events

Aspirin for the Primary Prevention of Cardiovascular Events: A Systematic Evidence Review for the U.S. Preventive Services Task Force - PubMed - NCBI
CONCLUSIONS:
In primary prevention populations, aspirin modestly reduces nonfatal MI/coronary events and major CVD events, but also increases major GI bleeding risk. More precise real-world estimates for bleeding events, including major GI bleeding events and hemorrhagic stroke, are necessary to calculate the net benefit. At some absolute risk for 10-year CVD events, this absolute CVD benefit could potentially outweigh the bleeding risks. Models to identify these populations are needed.
 

Mito

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Dec 10, 2016
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Strengths and limitations of this review
We undertook comprehensive searches and thorough systematic review methods following recognised guidelines. We evaluated all studies and re-analysed meta-analytic findings. We limited searches to 2008 or after, nevertheless because of the intense interest that this subject has generated and the cataloguing of all primary research in so many systematic reviews, we are confident that we have not omitted any major relevant randomised controlled trials or systematic reviews. A further limitation is our reliance on study level systematic reviews in which person years of follow up are not accurately ascertainable. However, estimates of number of events averted or incurred through aspirin use calculated from data in study level meta-analyses did not differ substantially from estimates based on IPD level meta-analyses, where person years of follow up were more accurate.
 

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