Abstract PS4-09-13: Elevated Genomic Risk and Treatment Gaps in Black Patients with HR+ Early Breast Cancer: A MammaPrint-Based Retrospective Analysis

Abstract Background: Black women with hormone receptor-positive (HR+) early-stage breast cancer (EBC) experience a 38% higher mortality rate than White women, even after accounting for socioeconomic factors and healthcare access. Biologic and genomic differences are increasingly recognized as contributors to this disparity. Gene expression (GE) assays help predict recurrence risk and guide treatment decisions. However, evidence suggests some of these tests may underestimate risk in Black patients. MammaPrint, however, among GE tools, has demonstrated enhanced sensitivity in identifying high-risk disease in Black women, suggesting improved risk stratification in this population. Objective: To analyze MammaPrint risk classifications and treatment patterns in a real-world, exclusively Black cohort with HR+ early breast cancer. We examined associations with tumor stage, molecular subtype, and chemotherapy use, and compared findings with historic, predominantly White populations such as the MINDACT trial. Methods: We conducted a retrospective chart review of 118 self-identified Black/African American women aged ≥18 years with Stage I-III HR+ breast cancer who had MammaPrint testing done and had clinic visits between October 2024 to June 2025 at West Cancer Center and University of Tennessee in Memphis, Tennessee. One patient with Stage IV disease was grouped with Stage III for analysis. Tumor characteristics, molecular subtype, and treatment data were extracted from electronic medical records. Statistical analyses included descriptive statistics, Chi-square, Fisher’s Exact, and Cochran-Armitage trend tests. This pilot phase of 118 patients will be expanded to approximately 1,000 patients from the same two clinics seen in the past year to further evaluate correlations and validate findings. Results: Among 118 patients, 65 (55.1%) were classified as High Risk and 53 (44.9%) as Low Risk by MammaPrint. The mean age was 62.5 years (SD = 12.9). MammaPrint risk was not significantly associated with tumor stage (P = 0.07), though a significant trend showed 50% of Stage I, 67% of Stage II, and 88% of Stage III/IV patients classified as High Risk (P trend = 0.02). MammaPrint risk correlated strongly with molecular subtype (p 0.001), with 94.5% of Low Risk patients having Luminal A tumors versus 87.8% of High Risk patients having Luminal B tumors.Despite over half the cohort classified as High Risk, only 28% received neoadjuvant chemotherapy and 9.3% received adjuvant chemotherapy. These low treatment rates raise concerns about potential undertreatment, consistent with FLEX registry findings.In contrast, the MINDACT trial, with a largely White population, reported a High Risk proportion of 35.8% in HR+ early breast cancer patients. This suggests the genomic risk burden may be substantially higher among Black women, underscoring the need for more inclusive validation of genomic tools and equitable precision oncology application. Conclusions: In this exclusively Black cohort, MammaPrint identified a significantly higher proportion of High Risk patients than historic White-majority populations, such as in MINDACT. The majority of High Risk tumors were Luminal B; however, chemotherapy use was low, highlighting gaps in clinical application of genomic data. These low rates may reflect the predominant use of Oncotype to guide chemotherapy decisions, as it remains the standard of care. These results emphasize the importance of MammaPrint in risk stratification for Black patients and the need to address disparities in guideline-based treatment. Citation Format: S. Sareen, A. Naik, C. Kent, G. Vidal, A. Hendrix, P. Kheirkhah Rahimabad, A. Bagchi. Elevated Genomic Risk and Treatment Gaps in Black Patients with HR+ Early Breast Cancer: A MammaPrint-Based Retrospective Analysis 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 PS4-09-13.