Low-dose aspirin and breast cancer risk: Results from a randomized trial

B33

The Women’s Health Study trial reported a lack of effect of low-dose aspirin (100-mg every other day) on cancer risk, including invasive breast cancer, over an average of 10 years of treatment and follow-up. Outstanding issues that have not been addressed previously for breast cancer include whether low-dose aspirin might reduce the risk in subgroups according to baseline risk factors or tumor characteristics. We randomly assigned 39,876 women aged 45 and older and who were free of cancer and cardiovascular disease to receive 100-mg of aspirin every other day (19,934 participants) or placebo (19,942 participants) from 1993 to 1996. Participants were followed through March 31, 2004. Using intent-to-treat analysis, we compared the risk for breast cancer after randomization between the groups and calculated hazard ratios and 95% confidence intervals using Cox proportional hazards regression models. Low-dose aspirin had no significant effect on the risk for total (762 vs. 779 cases, hazard ratio = 0.98; 95% confidence interval: 0.88, 1.08) or invasive breast cancers (608 vs. 622 cases, hazard ratio = 0.98; 95% confidence interval: 0.87, 1.09) compared with placebo. There was also no significant effect of low-dose aspirin on the risk for invasive breast cancers by categories of baseline risk factors for breast cancer, or by tumor characteristics at diagnosis, including tumor size, lymph node metastasis, histology, histologic grading and differentiation, or hormone receptor status. These results suggest that 100-mg aspirin taken every other day over 10 years does not have a chemopreventive effect on breast cancer.