Abstract B91: Long-term aspirin use and the risk of total, fatal and aggressive prostate cancer in a prospective cohort of health professionals, 1988-2004.

Abstract

Abstract B91 Background Experimental studies support aspirin in the chemoprevention of prostate cancer and an increasing body of epidemiological evidence supports a modest inverse association between regular aspirin use and prostate cancer risk, with stronger and more consistent associations for advanced disease. Methods In a prospective cohort study of 48,834 health professionals aged 40-75 years at baseline, we evaluated long-term aspirin use and the incidence of total, fatal and aggressive (Gleason 8-10 or T3b-T4 or N1 or M1) prostate cancer from 1988-2004. We used Cox proportional hazards regression to evaluate the risk of prostate cancer associated with cumulative averages of aspirin frequency (days/week), quantity (adult-strength tablets/week), and total duration (years) after multivariable adjustment for age, race, family history and other predictors of prostate cancer risk and mortality in the Health Professionals Follow-up Study cohort. Combined aspirin patterns were evaluated through the number of aspirin tablet-years, a measure of adult-strength tablets/day multiplied by number of years in frequent users (> 6 days/week). Results A total of 4,437 men were diagnosed with prostate cancer over 697,669 person-years of follow-up during the 16-year study period. Aspirin use was not associated with total prostate cancer risk, although non-significant inverse associations were observed for longer durations (> 5 years, HR: 0.90, 95% CI: 0.80, 1.02) after excluding PSA-detected disease (T1c). For fatal disease (n=347), mixed patterns emerged but there were no significant associations with aspirin frequency, quantity or duration. For aggressive prostate cancer (n=619), when compared to non-users, men who took aspirin > 4 days/week experienced a non-significant 20% reduction in risk (95% CI: 0.49, 1.32), while those taking > 4 adult-strength tablets had a non-significant 19% lower risk (95% CI: 0.57, 1.15) and men with a duration of > 5 had a non-significant 17% reduction (95% CI: 0.65, 1.05). A lower number of days/week, tablets/week and shorter durations yielded estimates that were similar in magnitude and statistically significant (p<0.05) but there was no evidence of a dose-response effect. Single and combined parameters (aspirin tablet-years) both suggest a threshold, rather than dose-response effect of aspirin on aggressive prostate cancer risk. Analytical approaches to address a potential bias from higher PSA screening among aspirin users, including stratification, adjustment for screening, and exclusion of screen-detected disease, did not change the overall conclusions. Conclusions We observed a suggestive reduced risk of aggressive prostate cancer associated with measurements of aspirin use in a large, prospective cohort of health professionals. Our data support earlier observations of modest inverse associations with advanced prostate cancer. Citation Information: Cancer Prev Res 2008;1(7 Suppl):B91.