LAUSR

Background: Forkhead box protein A1 (FOXA1) plays a key role in determining estrogen receptor (ER) function and mammary ductal development and may repress the basal cell phenotype during differentiation of breast epithelium. While reproductive factors are known to influence breast cancer risk depending on the subtypes, data on the association of tumor FOXA1 protein expression and reproductive characteristics are very limited. Methods: Tissue microarrays comprising surgical tumors from 638 women (466 African-American [AA] and 172 European-American [EA], aged 20-75 years) with primary breast cancer in the Women’s Circle of Health Study (WCHS) were analyzed for FOXA1 expression by immunohistochemistry and automated image analysis. In-person interviews were conducted to obtain data on demographics, medical and family histories, and reproductive and menstrual histories. Logistic regression was performed for FOXA1 positivity (>10% cells with strong staining) with menopausal status, age at menarche, age at first live birth, parity, and breastfeeding, adjusting for age at diagnosis, family history of breast cancer, and history of benign breast disease. Results: FOXA1 expression was higher in tumors from EA compared to those from AA women (80% vs. 70% positivity, P=0.011). FOXA1 expression was highly correlated with ER positivity (88% positive in ER+ and 26% in ER- breast cancer among AA women; 90% and 29% respectively among EA women; both P Conclusion: In AA women, a higher number of live births, which has been related to greater risk of ER- breast cancer, is associated with lower FOXA1 expression. Because FOXA1 promotes luminal and represses the basal differentiation, respectively, the effects of parity on expression of FOXA1 may be the link whereby it increases risk of ER- breast cancer. (Funding: NIH P01CA151135, R01CA100598, R01CA185623, P30CA072720, K07CA201334; US Army Medical Research and Material Command DAMD-17-01-1-0334; the Breast Cancer Research Foundation; and the Philip L. Hubbell family) Citation Format: Ting-Yuan David Cheng, Rochelle Payne Ondracek, Song Yao, Wiam Bshara, Thaer Khoury, Gary R. Zirpoli, Warren Davis, Elisa V. Bandera, Michael Higgins, Christine B. Ambrosone. Breast tumor FOXA1 protein expression and reproductive characteristics among African-American and European-American women [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4998. doi:10.1158/1538-7445.AM2017-4998