Abstract PS4-09-22: Uneven Progress: A Two-Decade Analysis of Regional Variations in Breast Cancer Mortality in the United States

Abstract Background: Breast cancer (BC) remains a leading cause of cancer death among U.S. women. Despite significant advances in BC screening and treatment leading to declining national mortality rates, regional disparities in healthcare access and socioeconomic factors may contribute to uneven progress across U.S. geographic regions. This study aims to quantify these disparities and identify areas where tailored interventions may be needed. Method: We conducted a retrospective cohort study using the Centers for Disease Control and Prevention (CDC) WONDER database (ICD-10). We identified all women who died of BC (C50), as the underlying cause of death (UCD) between 2000 and 2023. Age-adjusted mortality rates (AAMRs) were calculated per 100,000 persons, standardized to the 2000 U.S. Census, and stratified by the census region [Northeast (NE), Midwest (MW), South (S), and West (W)]. AAMRs were analyzed using linear regression models over a 24-year period to determine average annual reduction (AAR) and overall trends. 95% confidence intervals (CIs) were used to assess the reliability of mortality rate estimates and validate the linear regression analysis. Regional comparisons were conducted to assess geographic disparities in mortality outcomes. Results: At the national level, a total of 995,078 deaths from BC were identified, with an overall AAMR of 21.8 (95% CI: 20.7 - 22.9), and region-specific AAMRs of 21.8 (95% CI: 21.3 - 22.3) in the NE, 22.4 (95% CI: 21.9 - 22.8) in the MW, 22.3 (95% CI: 21.9 - 22.7) in the S, and 20.8 (95% CI 20.4 - 21.3) in the W.Between 2000 and 2023, the overall AAMR declined by 31.3%, with a consistent national AAR of 1.30% per year. Regional AAMRs declined by 39.4% from 27.9 (95% CI: 27.4 - 28.5) to 16.9 (95% CI: 16.5 - 17.3) with an AAR of 1.68% per year (95% CI: 1.64% to 1.72%) in the NE, 33.2% from 27.7 (95% CI: 27.2 - 28.3) to 18.5 (95% CI: 18.1 - 18.9) with an AAR of 1.44% per year (95% CI: 1.34% to 1.54%) in the MW, 24.4% from 26.2 (95% CI: 25.8 - 26.7) to 19.8 (95% CI: 19.5 - 20.1) with an AAR of 1.02% per year (95% CI: 0.88% to 1.15%) in the S, 27.7% from 25.3 (95% CI: 24.7 - 25.9) to 18.3 (95% CI: 18 - 18.7) with an AAR of 1.20% per year (95% CI: 1.05% to 1.35%) in the W. Conclusion: This is one of the largest population-based studies analyzing nearly one million deaths from breast cancer in women over the past two decades. While there has been significant national progress in breast cancer mortality reduction across all U.S. regions (31.3% decline, 1.30% annually), substantial regional disparities persist. The NE is leading the nation in mortality reduction (39.4% reduction, 1.68% annually) while the S showed the most modest gains (24.4% reduction, 1.02% annually). These findings underscore the need for region-tailored strategies—enhancing screening outreach, closing healthcare access gaps, and targeting socio-demographic risk factors—to ensure mortality reductions are equitably realized nationwide. Citation Format: A. Al-Zubaidi, A. Robinson, G. Whitman, T. Moseley, B. Adrada, E. Cohen. Uneven Progress: A Two-Decade Analysis of Regional Variations in Breast Cancer Mortality in the United States [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 PS4-09-22.