Regular aspirin use, breast tumor characteristics and long-term breast cancer survival.

Epidemiologic data, supported by experiments, suggest aspirin may improve survival in breast cancer patients. However, recent trials reported a lack of protection, though the length of intervention was limited. Among 10,705 stages I-III breast cancer patients in the Nurses' Health Studies (NHS/NHSII), we examined the associations between post-diagnostic aspirin use and long-term breast cancer survival. During up to 34 years of follow-up, regular post-diagnostic aspirin use was associated with a 38% and 28% lower risk of breast cancer-specific and total mortality. Associations were more evident with longer duration of post-diagnostic aspirin use but attenuated with higher stage and older age at diagnosis. Pre-diagnostic long-term aspirin use was associated with the downregulation of tumor proliferation pathways in NHS/NHSII and the aspirin-gene-expression-signature predicted better survival in METABRIC. Our study highlighted the need for trials with longer duration and suggested that aspirin use before diagnosis may alter the tumor-microenvironment towards a less proliferative type.