Abstract P3-12-01: Regular aspirin use, breast tumor characteristics and long-term breast cancer survival
Authors: Peng Cheng , Holmes Michelle D. , Wang Tengteng , Harris Alexandra , Chen Wendy , Brantley Kristen , Heng Yujing J , Bret-Mounet Vanessa C. , Baker Gabrielle M , Rosner Bernard , Willett Walter , Tamimi Rulla , Eliassen A. Heather 
Published: March 2022

Abstract
Background: Experimental evidence suggests that aspirin may inhibit breast tumor growth and reduce invasiveness of breast cancer cells. In large population-based studies (including our own), post-diagnostic aspirin use was associated with reduced breast cancer-specific and all-cause mortality. Here, we have extended our prior study with an additional 10 years of follow-up (3,785 more breast cancer cases) and investigation of the molecular underpinnings of the role of aspirin in breast cancer prognosis. Methods: Our study included 7,949 women diagnosed with stage I, II or III breast cancer from the Nurses’ Health Study (NHS) and NHSII. Cox proportional hazards regression was used to compute the multivariate hazard ratio (HR) for death, adjusting for tumor characteristics, treatment information and lifestyle factors. Post-diagnostic aspirin use was obtained at least 12 months after diagnosis and updated at every 2-year follow-up interval. We also evaluated the association between post-diagnostic aspirin use and survival according to tumor characteristics. Estrogen receptor (ER), insulin receptor (IR), PTEN, and Ki67 protein expression was evaluated by immunohistochemistry. PIK3CA mutation status was determined via polymerase chain reaction and pyrosequencing. In an exploratory analysis to identify functional enrichment of biologic pathways associated with long-term pre-diagnostic aspirin use (ever use of aspirin for ≥10 years with &gt;2d/wk), we used a competitive gene-set testing procedure in a subgroup of cases with gene expression data (N=453). In this subset, we also computed the abundance of immune cell infiltration (B cell, CD4+ T cell, CD8+T cell, macrophage, neutrophil and dendritic cell) using Tumor IMmune Estimation Resource (TIMER). Results: During a median follow-up of 12 years after breast cancer diagnosis, we documented 2,502 deaths, including 1,373 from breast cancer. Compared with nonusers, women who regularly used aspirin after diagnosis had lower breast cancer-specific mortality: HR for 1, 2-5, 6-7 days of aspirin use per week were 0.65 (95% CI: 0.49, 0.86), 0.41 (95% CI: 0.29, 0.57) and 0.61 (95% CI: 0.47, 0.78) for, respectively (p-trend&lt;0.0001). The association did not differ statistically by PTEN loss, PIK3CA mutation, or expression of IR (PI3K—AKT—mTOR), ER or Ki67 expression (proliferation pathways), or immune cell infiltration of the primary tumors (p-heterogeneity&gt;0.05). Long-term regular aspirin use before diagnosis was associated with the downregulation of pathways related to inflammation (INF-α, INF-γ, and TNF-α), PI3K—AKT—mTOR signaling (mTOR and PI3K—AKT), and other proliferation (E2F and myc targets) in primary breast tumors and/or normal-adjacent tissues (FDR≤0.05). Long-term regular aspirin use prior to diagnosis was also associated with higher CD8+T cell (mean±SD=0.20±0.02 for non-users and 0.21±0.02 for users, p=0.01) and macrophage (mean±SD=0.05±0.03 for non-users and 0.06±0.02 for users, p=0.0002) relative abundance in primary tumors. Conclusion: Regular aspirin use after breast cancer diagnosis was associated with lower risk of breast cancer-specific and total mortality. The association between aspirin and mortality did not differ by molecular characteristics of primary tumors. Long-term aspirin use prior to breast cancer diagnosis was associated with downregulation of inflammatory and proliferation pathways and higher immune cell infiltration of CD8+ T cells and macrophages in breast tumors. Taken together, our large-scale population-based analysis with long-term of follow-up highlight the potential benefit of aspirin as a secondary prevention strategy across different tumor molecular characteristics.
Citation Format: Cheng Peng, Michelle D. Holmes, Tengteng Wang, Alexandra Harris, Wendy Chen, Kristen Brantley, Yujing J Heng, Vanessa C. Bret-Mounet, Gabrielle M Baker, Bernard Rosner, Walter Willett, Rulla Tamimi, A. Heather Eliassen. Regular aspirin use, breast tumor characteristics and long-term breast cancer survival [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-12-01.