Aspirin for the prevention of cancer incidence and mortality: Systematic evidence reviews for the U.S. preventive services task force

Background: Cancer is the second leading cause of death in the United States. Purpose: To conduct systematic reviews of aspirin and 1) total cancer mortality and incidence in persons eligible for primary prevention of cardiovascular disease (CVD) and 2) colorectal cancer (CRC) mortality and incidence in persons at average CRC risk. Data Sources: MEDLINE, PubMed, and the Cochrane Central Register of Controlled Trials through January 2015 and relevant references from other reviews. Study Selection: Trials comparing oral aspirin versus placebo or no treatment in adults aged 40 years or older were included. Two investigators independently reviewed abstracts and articles against inclusion and quality criteria. Data Extraction: Data from 20 good- or fair-quality trials were abstracted by one reviewer and checked by another. Data Synthesis: In CVD primary prevention trials, cancer mortality (relative risk [RR], 0.96 [95% CI, 0.87 to 1.06]) (10 trials; n = 103 787) and incidence (RR, 0.98 [CI, 0.93 to 1.04]) (6 trials; n = 72 926) were similar in aspirin and control groups over 3.6 to 10.1 years. In CVD primary and secondary prevention trials, 20- year CRC mortality was reduced among persons assigned to aspirin therapy (RR, 0.67 [CI, 0.52 to 0.86]) (4 trials; n = 14 033). Aspirin appeared to reduce CRC incidence beginning 10 to 19 years after initiation (RR, 0.60 [CI, 0.47 to 0.76]) (3 trials; n = 47 464). Limitations: Most data were from clinically and methodologically heterogeneous CVD prevention trials. Outcome assessment and follow-up length varied across studies. Data on non- CRC cancer types and subgroups were limited. Conclusion: In CVD primary prevention populations, aspirin's effect on total cancer mortality and incidence was not clearly established. Evidence from CVD primary and secondary prevention studies suggested that aspirin therapy reduces CRC incidence and perhaps mortality approximately 10 years after initiation.