Inequities in breast cancer mortality with contributing cardiometabolic disorders among U.S. women aged ≥45 years, 1999–2024.

e12704 Background: While breast cancer survival has improved, cardiometabolic disorders including obesity, diabetes, cardiovascular diseases (e.g., hypertension, thrombosis, cardiomyopathy, stroke, heart failure), liver disorders (e.g., non-alcoholic steatohepatitis, hepatic steatosis), and certain gynecological conditions are increasingly recognized as competing risks for mortality. Trends in deaths with breast cancer as the underlying cause and cardiometabolic disorders as contributing causes remain poorly characterized, particularly across demographic and geographic subgroups. This analysis focuses on women ≥45 due to low mortality counts (n = 2,988) in younger women. Methods: We analyzed U.S. mortality data (1999–2024) for women aged ≥45 with breast cancer as the underlying cause and cardiometabolic disorders as contributing causes. Age-adjusted mortality rates (AAMR) per 100,000 were calculated. Joinpoint regression estimated Annual Percent Change (APC) and average annual percent change (AAPC) to evaluate trends stratified by race, U.S. census region, and urbanization. Results: A total of 167,620 deaths occurred among women aged ≥45 years during 1999–2024 (overall AAMR 8.40 per 100,000). Mortality declined modestly from 1999–2011 (APC −0.39%, p = 0.01), reaching an AAMR of 7.51 in 2015, before reversing. The sharpest increase occurred during 2018–2021 (APC +6.88%, p < 0.01), with AAMRs rising from 7.87 in 2018 to 9.58 in 2021 and remaining elevated through 2024 (AAMR 9.90). Substantial racial disparities were observed; Black women consistently exhibited a mortality burden approximately twofold higher than White women. From 2015–2024, mortality among Black women rose significantly (APC +3.56%, p < 0.001), reaching an AAMR of 15.72 in 2024, compared with 9.54 among White women. Regionally, the South showed a sustained increase since 2015 (APC +4.91%, p < 0.001) with the highest 2024 AAMR (11.36). The West also saw a post-2016 rise (APC +5.38%, p < 0.001), while the Northeast and Midwest showed no significant net increase. Nonmetropolitan areas faced the most concerning trends: micropolitan and noncore areas saw increases beginning in 2017 (APC +6.53% and +13.35%, respectively), with 2020 AAMRs of 10.68. Medium metropolitan counties also rose post-2016 (APC +5.47%, p < 0.001). Conversely, large central and fringe metropolitan areas showed long-term declines (AAPC −0.15% and −0.14%, respectively) with no significant net increase. Conclusions: Mortality for breast cancer with cardiometabolic contributions is rising among women ≥45, disproportionately affecting Black women, the South, and non-metropolitan areas, highlighting the need for targeted interventions in cardio-oncology, survivorship, and lifestyle strategies including structured exercise.