Abstract PS4-12-09: Racial and Ethnic Disparities in Enrollment to Breast Cancer Clinical Trials from 2000 to 2025

Abstract Background: Breast cancer (BC) remains the most common malignancy among women worldwide and is the leading cause of cancer-related mortality. Despite significant advances in treatment and an increase in clinical trial (CT) activity over the past two decades, equitable access to trials has not kept pace. Racial and ethnic disparities in trial enrollment persist, limiting the generalizability of findings and perpetuating outcome gaps. Non-Hispanic Black women, in particular, face higher BC mortality despite similar or lower incidence compared to non-Hispanic White women. Understanding trends in CT representation is essential to addressing these inequities. This study aimed to evaluate global enrollment patterns by race and ethnicity (R/E) in completed BC CTs. Methods: We conducted a retrospective analysis of completed BC CTs registered on clinicaltrials.gov between 1/1/2000 and 6/1/2025. A total of 283 phase III-IV interventional studies were included. Trials were reviewed for reporting of R/E. The key outcome was to evaluate enrollment by R/E, in 5-year intervals to assess temporal trends. For each trial, the proportion of participants (pts) by R/E was extracted, and aggregate enrollment ratios were calculated across all reporting trials. Descriptive statistics were used for data analysis. Results: Of the 283 eligible trials, 120 (42%) reported race and 63 (22%) reported ethnicity. Most studies were conducted in North America and Europe. Among trials reporting race, White pts were the most represented, while Native Hawaiian and Pacific Islander pts were the least represented. Temporal trends demonstrated a decrease in White race enrollment from 88.9% (2000-2005) to 66.7% (2015-2021), alongside an increase in Asian enrollment from 4.5% to 21.5% over the same period. Among the 63 trials reporting ethnicity, 62 included non-Hispanic and 56 included Hispanic pts. Non-Hispanic individuals accounted for 81.4% of total enrollment across these trials. Overall, 75% of all pts identified as White, while Black pts accounted for only 3.4. Notably, 15 trials reported only a single race, often reflecting geographic enrollment patterns. Conclusions: Over the past 25 years, Black and Hispanic patients remained underrepresented in BC CTs. While modest improvements have occurred over time, particularly in Hispanic and Asian enrollment, persistent disparities limit the generalizability of trial findings and hinder progress toward equitable cancer care. This analysis is limited by the lack of standardization in how R/E are defined and reported, absence of geographic or population-adjusted benchmarks, and reliance on registry-reported data may underestimate disparities or mask regional variation. Greater transparency and standardization in demographic reporting, along with proactive efforts to diversify CT participation, are essential to ensure all patient populations are equitably represented in BC research. Citation Format: V. Andion Camargo, F. Akkoc Mustafayev, K. Qidwai, M. Jaramillo, S. Lin, Z. Sarfraz, L. S. Spiegelman, K. Mustafayev, M. A. Ganiyani, M. S. Ahluwalia, R. L. Mahtani. Racial and Ethnic Disparities in Enrollment to Breast Cancer Clinical Trials from 2000 to 2025 abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS4-12-09.