Aspirin use and mortality in men with localised prostate cancer: A cohort study.

Abstract

5084 Background: Cyclooxygenase-2 (COX-2) expression in prostate cancer has been associated with high grade tumours and poorer prognosis. Use of aspirin, a COX-2 inhibitor, has been associated with reduced prostate cancer mortality in some studies. These studies have not, however, provided information on the dose and timing of aspirin use. Methods: National Cancer Registry Ireland data was used to identify men with stage I-III prostate cancer (ICD10 C61) diagnosed 2001-2006. Aspirin use in the year preceding prostate cancer diagnosis was identified from linked prescription refill data (General Medical Services) and stratified by dose (low ≤75mg, high >75mg) and dosing intensity (proportion of days in that year with aspirin supply available). Cox proportional hazards models, adjusted for age, smoking status, year of incidence, comorbidity score, Gleason score, tumour size, pre-diagnostic statin use, and receipt of radiation (time varying) were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for associations between aspirin use and all-cause and prostate cancer-specific mortality. Interactions with tumour characteristics were examined. Results: 2,936 men with stage I-III prostate cancer were identified (aspirin users, N=1,131; 38.5%). Median patient follow-up was 5.5 years. In multivariate analyses, aspirin use was not associated with a significant reduction in prostate cancer-specific (HR 0.90, 95% CI 0.68-1.20) or all-cause mortality (HR 0.98, 95% CI 0.84-1.15). In dose response analyses aspirin use was associated with a significantly lower risk of prostate cancer-specific mortality in men receiving >75mg of aspirin (HR 0.59, 95% CI 0.35-1.00, p=0.048) but not ≤75mg aspirin (HR 1.01, 95% CI 0.75-1.37, p=0.938). Stronger associations were also observed in men with higher aspirin dosing intensity or a Gleason score >7. Conclusions: Pre-diagnostic aspirin use, measured using objective prescription refill data, was associated with a significant reduction in prostate cancer-specific mortality in men with stage I-III prostate cancer receiving >75mg of aspirin. These results confirm previous findings, and provide important new information regarding the dose of aspirin associated with survival benefit.