Abstract 4635: Analysis of post-partum breast tissue to understand early onset breast cancer
Authors: Ogony Joshua , Radisky DereK C. , Degnim Amy C. , Frost Marlene , Hoskin Tanya L. , Heckman Michael G. , White Launia J. , Sherman Mark E. 
Published: September 2020

Abstract
Background: Parity reduces risk of late onset breast cancer (BC), but childbirth is associated with a transient rise in BC risk. In a prior analysis of normal breast tissues donated for research to the Komen Tissue Bank (KTB), we reported that numbers of lobules (the primary structures from which BCs arise) are increased among parous versus nulliparous women. To further define the histological features that may be related to the transient rise in post-partum BC risk, we performed an expanded histologic review of 757 breast tissues donated to the KTB by women ≤45 years of age and compared lobule number, acinar count per lobule, and abundance of immune cells, and specifically plasma cells, between nulliparous and parous women.
Methods: We assessed digital scans of H&E stained tissue sections of KTB tissues for total number of lobules, and evaluated acini / lobule (ordinal categories) and lobule span (um) for ≤10 lobules per section. Masked to epidemiologic data, we subjectively assessed images including ≥5 lobules for the presence of benign breast disease (BBD), ≥3 plasma cells per section and increased immune cells in lobules. We compared parous women according to time since last birth (≤5 years or &gt;5 years) to nulliparas (referent) using age-adjusted regression models appropriate for data type (count, continuous, ordinal, or categorical).
Results: Compared to nulliparous women, parous women ≤5 years of a birth had a 1.83-fold increase in lobule counts (95% confidence interval [CI]: 1.47-2.28, P&lt;0.001), increased plasma cells in lobules (OR=1.86; 95% CI: 1.08-3.18, P&lt;0.025), and subjectively, increased immune cells in lobules (OR=2.46, 95% CI: 1.39-4.36, P&lt;0.002). Comparisons of parous women ≥5 years post-partum to nulliparas revealed a 1.83-fold increase in numbers of lobules (95% CI: 1.42-2.36, P&lt;0.001); however, lobule span in parous women was 0.89 times that of nulliparous women (95% CI: 0.80-0.99, P=0.037) and other features assessed did not show statistically significant differences.
Conclusion: Histologically, normal breast tissues reveal persistently increased lobule counts and increased plasma cells and inflammation for ≤5 years post-partum compared with nulliparous women, although other lobular features decrease between ≤5 and &gt;5 years after a birth. Future molecular studies will define how these changes in the epithelium and microenvironment during the post-partum period may inform mechanisms that mediate the transient increase in BC risk after childbirth and the reduction in BC risk that occurs later in life.
Citation Format: Joshua Ogony, DereK C. Radisky, Amy C. Degnim, Marlene Frost, Tanya L. Hoskin, Michael G. Heckman, Launia J. White, Mark E. Sherman. Analysis of post-partum breast tissue to understand early onset breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4635.