Abstract BACKGROUND: African American (AA) women have a 4-5 fold greater risk of death from estrogen and/or progesterone receptor positive (ER/PR positive) breast cancer compared to non-Latina white (white) women, even after controlling for stage at diagnosis, treatment, and other prognostic factors. The purpose of this study is to examine whether there are racial differences in biologic mechanisms typically activated in ER/PR positive breast cancer and whether they might lead to a higher rate of distant metastases and/or resistance to endocrine therapies. METHODS: Eligible cases -AA and white women, aged 20-79, with a new diagnosis of stage I-III ER+ breast cancer- are being recruited from 3 cancer institutions in Chicago. Control subjects -AA and white women presenting for a screening mammogram without breast symptoms and no history of cancer- have been recruited from the corresponding mammography centers. We are collecting serum from AA and white cases and controls in order to conduct a metabolomic analysis to identify oncometabolites that might promote aggressive phenotypes in ER/PR breast cancer cells. Serum collection is taking place prior to breast surgery or initiation of any neoadjuvant or adjuvant therapies to ensure that our findings are not due to treatment effects on metabolites. RESULTS: To date, we have enrolled 175 out of 300 planned study participants. Recruitment will be completed by January 2019, and preliminary metabolomic data will be presented. We will explore associations between candidate oncometabolites and neighborhood socioeconomic deprivation as well as individual patient and tumor characteristics typically related to poor outcomes in AA women with BC. Analyses will adjust for tumor intrinsic subtype (Luminal A vs. Luminal B) to account for known differences in molecular pathways by tumor subtype. We hope to identify biochemical differences in serum that could help to explain the unanswered question regarding why AA patients with ER/PR positive breast cancer or more likely to die from the disease compared to their white counterparts. Note: This abstract was not presented at the meeting. Citation Format: Ashlie M. Santaliz Casiano, Zeynep Madak-Erdogan, Oana Danciu, Hariyali Patel, Landan Banks, Jermya Buckley, Garth Rauscher, Anita Fareeduddin, Elonia Martin, Archana Bargaje, Carlos Garcia, Lauren Schulte, Deanna Taiym, Julie Kim, William Gradishar, Scott Hegerty, Jonna Frasor, Kent Hoskins. Integrated molecular approach to identify biological factors contributing to breast cancer disparities in Chicago [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4208.