Abstract PS3-08-07: Comparative Analysis of Breast Cancer Index Testing in Hispanic and Non-Hispanic Populations

Abstract Background: Hispanic and non-Hispanic patients with breast cancer (BC) exhibit distinct clinicopathologic profiles that may impact treatment outcomes. The Breast Cancer Index (BCI) is a validated gene expression assay that assesses overall (0-10 years) and late (5-10 years) distant recurrence (DR) risk and predicts the likelihood of benefit from extended endocrine therapy (EET). This analysis compares BCI results and clinicopathologic features between Hispanic patients with hormone receptor positive (HR+) BC from Miami Cancer Institute (MCI) and non-Hispanic patients enrolled in the BCI Registry study. Methods: After IRB approval, we performed a retrospective review of patients treated at MCI with HR+ early-stage BC who underwent BCI testing as part of routine clinical care. (n=776). The BCI Registry is a prospective, multi-institutional study that enrolled over 3400 patients with early-stage HR+ BC to evaluate long-term clinical outcomes, decision impact, and medication adherence. Statistical analyses included Fisher’s exact test and the Cochran-Mantel-Haenszel (CMH) test to assess associations between different variables (clinicopathologic vs. ethnicity; clinicopathologic vs. BCI results), and the Breslow-Day (BD) test to evaluate whether ethnicity influences the association between clinicopathologic factors and BCI results (BCI Predictive and Prognostic groups). Results: The BCI Registry study included 2,406 non-Hispanic patients, while the MCI dataset comprised 408 self-identified Hispanic patients. Compared to non-Hispanic patients, Hispanic patients were more likely to identify as white (98% vs. 89%, p < 0.001), were younger (<50 years: 23% vs. 7%, p < 0.001), and were less likely to be postmenopausal (80% vs. 90%, p < 0.001). They were also less likely to start adjuvant endocrine therapy with an aromatase inhibitor (AI) (65% vs. 74%, p < 0.001) and more likely to switch therapy (20% vs. 13%). Clinicopathologic features were largely similar between groups, including tumor size, tumor grade, nodal status, and HER2 status. BCI Predictive results showed fewer Hispanic patients with a high likelihood of EET benefit (33% vs. 39%, p = 0.046), and BCI Prognostic results indicated a lower proportion categorized as High Risk for late distant recurrence (49% vs. 53%, p = 0.087). In BCI Predictive groups, stratified BD analysis revealed significant ethnic differences in associations between EET benefit and clinical variables, including age, surgery type (BD p = 0.01), menopausal status, tumor size, tumor grade, nodal status, and HER2 status (BD p < 0.001), with moderate effects for BMI (BD p = 0.042). In BCI Prognostic groups, strong ethnic stratification was observed for tumor size, tumor grade, nodal status, HER2 status, and surgery type (BD p < 0.001), with moderate effects for age (BD p = 0.03) and race (BD p = 0.013), suggesting ethnicity may influence how these factors relate to late distant recurrence. Conclusion: Hispanic patients with BC showed distinct clinical and molecular profiles compared to non-Hispanic patients, including younger age at diagnosis, differing endocrine therapy patterns, lower predicted benefit from EET, and more favorable tumor biology. These findings highlight the need to account for ethnic variability in personalized treatment planning and call for further research into individualized risk assessment in early-stage HR+ BC. However, these findings should be interpreted with caution given the retrospective, single institution nature of the Hispanic cohort. Long-term clinical outcomes from the MCI cohort will be reported in future analyses to better understand how BCI results correlate with real-world treatment decisions and patient outcomes. Citation Format: A. C. Sandoval-Leon, N. Siuliukina, Y. Liu, Y. Chamorro, N. Dempsey, M. M. Zerey, L. Dumeny, D. Tolman, P. Bhatt, L. Carcas, Y. Zhang, A. Anderson, K. Treuner, R. Mahtani. Comparative Analysis of Breast Cancer Index Testing in Hispanic and Non-Hispanic Populations [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 PS3-08-07.