Long-term aspirin use does not decrease the incidence of cancer in people who have not previously had cancer, compared to no aspirin use

Wu Q, Yao X, Chen H, etal. Long-term aspirin use for primary cancer prevention: An updated systematic review and subgroup meta-analysis of 29 randomized clinical trials J Cancer. 2020;11:6460-6473.

Review question

Is long-term aspirin use effective and safe in preventing cancer among those who have not previously had cancer? Do the effects differ based on the dosage of aspirin used, population, or follow-up duration?  

Background

Cancer cases and deaths from cancer are on the rise, despite up to 50% of cancer cases being deemed preventable. Currently available prevention strategies include: widely accepted tactics such as leading a healthy lifestyle and more debated approaches like aspirin use. Previous research on the use of aspirin for the purpose of cancer prevention has shown mixed results or was limited by factors such as study design, or the dosage, population, or cancer type being assessed. As such, more comprehensive research is needed to make more definitive conclusions about the relationship between aspirin and cancer prevention.  

How the review was done

This is a systematic review and meta-analysis of 29 randomized controlled trials. The studies were published between 1976 and 2018, and included a total of 200, 679 participants. Key features of the studies:

• On average, participants ranged between 44 and 74 years of age, had not previously had cancer, and could be categorized into the following categories: healthy, people with diabetes, people with cardiovascular disease (CVD) or an increased risk of CVD, people with an increased risk of cancer, or people with circulatory issues due to narrowed veins or blood clots in the deep veins.
• Participants took aspirin at varying doses. Generally, doses ranged between 81 mg and 1200 mg taken daily or every other day.  
• Researchers mainly evaluated the following outcomes: total cancer incidence, total cancer deaths, all-cause mortality (i.e. deaths from all causes during the study period), and bleeding.
• Results were compared to people in control groups who were not taking aspirin, meaning they were receiving no treatment or were taking a placebo. 
• On average participants took aspirin for a duration of 1-5 years, 5-10 years, or over 10 years, and therefore were followed between 1.8 years to 12 years. 

What the researchers found

The long-term use of aspirin did not reduce total cancer incidence, total cancer deaths, or all-cause mortality in people who had not previously had cancer, compared to no aspirin use. However, the use of aspirin increased people’s risk for a major bleed by 32% to 57%. The evidence for these outcomes is of high quality. Furthermore, moderate quality evidence indicated that total bleeding events increased by 33% to 74%. Similar results were seen regardless of aspirin dosage, population (e.g., healthy, has diabetes, has CVD, etc.), and follow-up durations.   

Conclusion

High to moderate quality evidence shows that long-term there is no preventative effect of aspirin on total cancer incidence, cancer mortality, or all-cause mortality, but that it does increase bleeding risk.