Daily Aspirin Use and Cancer Mortality in a Large US Cohort

Background A recent pooled analysis of randomized trials of daily aspirin for prevention of vascular events found a substantial reduction (relative risk [RR] = 0.63, 95% confidence interval [CI] = 0.49 to 0.82) in overall cancer mortality during follow-up occurring after 5 years on aspirin. However, the magnitude of the effect of daily aspirin use, particularly long-term use, on cancer mortality is uncertain. Methods We examined the association between daily aspirin use and overall cancer mortality among 100 139 men and women with no history of cancer in the Cancer Prevention Study II Nutrition Cohort. Cox proportional hazards regression models were used to estimate multivariable-adjusted relative risks (RRs) and 95% confidence intervals (CIs). Results Between 1997 and 2008, 5138 participants died from cancer. Compared with no use, daily aspirin use at baseline was associated with slightly lower cancer mortality, regardless of duration of daily use (for <5 years of use, RR = 0.92, 95% CI = 0.85 to 1.01; for ≥5 years of use, RR = 0.92, 95% CI = 0.83 to 1.02). Associations were slightly stronger in analyses that used updated aspirin information from periodic follow-up questionnaires and included 3373 cancer deaths (for <5 years of use, RR = 0.84, 95% CI = 0.76 to 0.94; for ≥5 years of use, RR = 0.84, 95% CI = 0.75 to 0.95). Conclusion These results are consistent with an association between recent daily aspirin use and modestly lower cancer mortality but suggest that any reduction in cancer mortality may be smaller than that observed with long-term aspirin use in the pooled trial analysis.