Authors: Maria Luisa Machado Heredia1,2 Alphi Kuriakose1,2 Huma Javaid1,3 Brian Menegaz 1,3 Alastair Thompson1,2,3 Bora Lim1,2 Affiliation 1Dan L. Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, TX 77030 2 Lester and Sue Smith Breast Center, Baylor College of Medicine, Houston, TX 77030 3 Department of Surgery, Baylor College of Medicine, Houston, TX 77030 Background and Purpose Increasing research data support the existence of barriers and discrepancies to oncology interventional clinical trial enrollment rate based on patients’ social-economic status. However, few studies examined if such discrepancy exists in observational trials. We hypothesize the enrollment discrepancy remains the same in specimen collection only protocols, and several factors including health literacy and religious belief contribute to such discrepancy. Methods Data was collected from March 1st, 2022, to July 7th, 2022, as part of an ongoing pilot study examining circulating tumor DNA (ctDNA) from patients diagnosed with stage IV metastatic breast cancer starting a new line of therapy treatment (BCM protocol number H- 48751). This study was selected as specimen collected is part of normally scheduled standard of care clinical labs and beyond informed consent does not require any additional patient commitment for participation. This study was performed across both county and private practice sites:1) Smith Clinic-Harris Health System 2) Baylor Saint Luke’s Medical center (BSLMC); respectively. Correlations for independent variables potentially affecting enrollment were assessed to estimate the association between patient participation and socio-economic factors like religious affiliation and level of formal education received. Free-form text responses were collected from patients who declined study participation. Results Fourteen eligible candidates were asked to participate in the observational trial to determine whether serial changes in ctDNA ratio correlate with the results of first monitoring patients via imaging at three months. Out of 14 patients approached, 5 patients (36%) declined. Interestingly, all five patients who declined were from Smith Clinic- Harris Health System, while all BSLMC patients agreed to enroll. Based on the free-text response of why patients declined the ctDNA study, we identified a total of 4 different categories: Language barriers, low health literacy, religious objection, and disinterest in research. Using these four categories, we continue to collect data to improve our understanding of barriers in observational trial enrollment. Conclusion Low literacy and other socioeconomic factors serve as barriers to enrollment in observational trials for patients who suffer from stage IV breast cancers. In our preliminary data, we also noted that these barriers are only relevant for patients who are treated at the county hospital. An investigation to recognize low literacy and religious affiliation as barriers to poor trial accrual is ongoing. Reasons to declining participation in observational trial. Citation Format: Maria L. Machado Heredia, Alphi Kuriakose, Brian A. Menegaz, Alastair M. Thompson, Bora Lim, Huma Javaid. Barriers to enrolling in observational trials for patients with stage IV breast cancer. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-08-03.