Daily treatment with aspirin for longer than 5 years reduces the long-term risk of colorectal cancer. A number of studies have suggested that long-term aspirin use may reduce the risk of several noncolorectal solid cancers, but clear evidence for a preventive effect is lacking.
This study investigated the possible effect of aspirin on reducing the risk of fatal cancer among patients with gastrointestinal and nongastrointestinal cancers. Data were obtained from randomized trials with aspirin, originally conducted on prevention of vascular events. Eligible trials with median duration of scheduled trial treatment of at least 4 years were identified in the medical literature.
Pooled results comparing the effect of aspirin and controls on deaths due to cancer showed 674 deaths due to cancer among 25,570 patients; aspirin significantly reduced the risk of cancer deaths (odds ratio, 0.79; 95% confidence interval [CI], 0.68-0.92; P = 0.003). Analysis of data on time of death available from 7 trials (23,535 patients, 657 cancer deaths) showed that a reduction in risk of death was apparent only after 5 years' follow-up for all cancers (hazard ratio [HR], 0.66; 95% CI, 0.50-0.87) and gastrointestinal cancers (HR, 0.46; 0.27-0.77; P values for both = 0.003). Three posttrial follow-up studies on the 20-year risk of death due to cancer (1634 deaths in 12,659 patients) showed that the reduction in risk by aspirin treatment compared with controls remained lower for all solid cancers (HR, 0.80; 95% CI, 0.72-0.88; P < 0.0001) and gastrointestinal cancer (HR, 0.65; 95% CI, 0.54-0.78; P < 0.0001). The greatest benefit was found with scheduled duration of trial treatment of >= 7.5 years for solid cancers (P = 0.003) and gastrointestinal cancers (P = 0.0001). Reductions in risk of death due to esophageal, pancreatic, brain, and lung cancer were evident only after a latent period of 5 years, whereas reductions in deaths due to stomach, colorectal, and prostate cancer were not observed until about 10 years. The benefit on the 20-year risk of death was limited to certain cancers, especially adenocarcinomas of lung (P = 0.04) and esophagus (P = 0.0001). The absolute reduction in risk of death due to cancer at 20 years increased with age, reaching 7.08% (95% CI, 2.42-11.74) at age 65 years or more. No increased benefit was found for aspirin doses greater than 75 mg daily and the effect was unrelated to gender or smoking.
These findings provide evidence that daily aspirin reduces the risk of death due to several common noncolorectal cancers during and after the trials, with consistent effects across different populations and benefit increasing with duration of treatment.