Aspirin and Risk of Specific Breast Cancer Subtype in Women with Diabetes.

Purpose: Low-dose aspirin was associated with a reduced risk of breast cancer in women with diabetes. However, whether the protective effect of aspirin varies as a function of the hormone receptor status of breast cancer remained an unanswered question. This study aims to explore the association between aspirin use and the risk of specific breast cancer subtypes in women with diabetes. Methods: Population-based retrospective cohort study of women with diabetes, using the Taiwan National Health Insurance reimbursement database (year 1998 to 2011). Patients diagnosed to have diabetes with new low-dose aspirin use (75-165 mg per day) for at least 28 days of prescription were identified as the study population, while patients without low-dose aspirin use were selected as controls. The main outcome measure was breast cancer by aspirin use and hormone receptor status. Results: We studied a total of 148,739 patients with diabetes. Their mean (standard deviation) age was 63.3 (12.8) years. During follow-up, a total of 849 breast cancers occurred, including 329 hormone receptor-positive and 529 hormone receptor-negative tumors. A total of 27,378 patients were taking aspirin. The reduction in risk with aspirin use was seen among those with hormone receptor-positive breast cancer (Hazard ratio [HR]: 0.73; 95% confidence interval [CI]: 0.59-0.91) but not for women with hormone receptor-negative breast cancer (HR: 0.88; 95% CI: 0.74-1.05). A cumulative dose of aspirin use of more than 8,600 mg was found to reduce the risk of hormone receptor-positive breast cancer by 31% (HR: 0.69; 95% CI: 0.50-0.97). A cumulative dose of aspirin use of more than 88,900 mg was found to reduce both the risk of hormone receptor-positive and negative breast cancer. Conclusion: These data add to the growing evidence that supports the use of low-dose aspirin as a potential chemopreventive agent for specific subtypes of breast cancer. Further studies are necessary to confirm these findings.