Abstract PS5-11-18: Racial and Ethnic Representation in Antibody-Drug Conjugate Clinical Trials for Breast Cancer: A 10-Year Review

Abstract Background: Breast cancer (BC) remains a leading cause of cancer-related morbidity and mortality among women. Despite therapeutic advances, racial and ethnic disparities persist in both clinical outcomes and research participation. Black women have a 40% higher mortality rate than White women despite similar incidence, and BC incidence is rising among Hispanic women. Antibody-drug conjugates (ADCs) have emerged as a transformative therapeutic class for patients with advanced and metastatic BC. As the use of ADCs expands, ensuring equitable representation in the clinical trials that support their approval is critical. This study aimed to evaluate racial and ethnic representation in interventional trials of ADC for BC. We specifically assessed the inclusion of underrepresented populations, the completeness of demographic reporting, and disparities in enrollment relative to the population most affected by the disease. Methods: We analyzed 25 interventional clinical trials investigating ADCs for the treatment of advanced or metastatic breast cancer (Stage III-IV) with publicly available results posted on ClinicalTrials.gov between 2015 and 2025. Trials were included if they investigated ADCs as the primary therapeutic agent and reported demographic data for enrolled patients. Key trial characteristics, including study phase, sponsor type, geographic region, and participant demographic data, were extracted. The primary objective was to assess racial and ethnic representation across trials and evaluate the completeness and consistency of demographic reporting. Descriptive statistics, including mean, median, standard deviation, and 95% confidence intervals, were calculated to summarize participant representation by race and ethnicity. Results: A total of 8,459 participants were included across 25 clinical trials. Most trials (72%, n=18) focused on Stage IV BC; 32% (n=8) also included patients with Stage III disease. All trials (n=25) reported racial demographics, while only 44% included data on ethnicity (n=11). White patients accounted for the highest median representation at 63.9% (n=4,993, 95% CI: 52.2-81.7), followed by Asian individuals at 20.5% (n=2,257, 95% CI: 6.7-40.0). Black patients were markedly underrepresented, with a mean enrollment of 2.2% (n=220, 95% CI: 1.4-3.6). Among the 11 trials that reported ethnicity, Hispanic patients represented a median of 8.1% (n=440, 95% CI: 4.3-17.6). Participants identified as “other” or not categorized represented 5.2% (n=989) of total enrollment. A majority of trials were multiregional (64%, n=16), with North America and Europe hosting most trial locations, 84% (n=21) and 56% (n=14) respectively. South America held only 20% (n=5) of clinical trials, with none in Africa. Most studies (84%, n=21) were industry-sponsored, while 16% (n=4) were led by academic or government institutions. Conclusion: This analysis reveals persistent underrepresentation of Black and Hispanic populations in clinical trials evaluating ADCs for BC, despite their disproportionate disease burden. The limited and inconsistent reporting of ethnicity, alongside broad racial categories that obscure the inclusion of American Indian, Pacific Islander, and multiracial participants further hampers comprehensive equity assessments. As a meta-research study limited to publicly reported data, our findings may underestimate disparities due to incomplete or inconsistent demographic documentation. Nonetheless, these results underscore the urgent need to prioritize representative enrollment and standardized demographic reporting in future ADC trials. Doing so is critical not only for ensuring equitable access to novel therapies, but also for enhancing generalizability of efficacy and safety outcomes across diverse patient populations in oncology. Citation Format: M. Jaramillo, Z. Sarfraz, C. Gillespie, S. Milan, S. Sukie, V. Andion Camargo, F. Akkoc Mustafayev, V. Podder, K. A. Qidwai, M. Ganiyani, M. S. Ahluwalia, R. Mahtani. Racial and Ethnic Representation in Antibody-Drug Conjugate Clinical Trials for Breast Cancer: A 10-Year Review 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 PS5-11-18.