Temporal changes in mortality among adults with breast cancer and diabetes mellitus in the United States.

1116 Background: Breast cancer and diabetes mellitus represent major and intersecting public health challenges in the United States. Although breast cancer mortality has declined over recent decades, the growing prevalence of metabolic comorbidities, particularly diabetes, may offset these gains. National patterns of mortality among individuals with both conditions remain incompletely defined. We evaluated long-term trends and demographic disparities in breast cancer--and diabetes-associated mortality from 1999 to 2023. Methods: We conducted a retrospective population-based analysis using the CDC Wide-Ranging Online Data for Epidemiologic Research (WONDER) Multiple Cause of Death database (1999–2023). Decedents aged 45–85+ years with breast cancer (ICD-10: C50) and diabetes mellitus (ICD-10: E10–E14) listed as underlying or contributing causes of death were included. Age-adjusted mortality rates (AAMRs) were calculated using the 2000 U.S. standard population. Trends were evaluated using Joinpoint regression to estimate annual percent change (APC) with 95% confidence intervals (CI). Analyses were stratified by age, sex, race/ethnicity, census region, and urbanization. Results: Between 1999 and 2023, 78,253 deaths occurred among adults aged 45–85+ years with breast cancer and diabetes mellitus (1.6% male, 98.4% female). Overall AAMRs increased modestly from 2.64 to 2.84. Females consistently exhibited higher mortality than males (5.00 vs 0.13 in 2023). Non-Hispanic Black individuals had the highest AAMRs (5.61), whereas non-Hispanic American Indian/Alaska Native, Asian, and Native Hawaiian/Pacific Islander populations had the lowest (2.05). Mortality counts were greatest in the Southern region and lowest in the Northeast. Nationally, AAMRs declined from 2004 to 2018 (APC −1.82%; 95% CI, −2.12 to −1.51; P<0.001), followed by a sharp increase from 2018 to 2021 (APC 12.30%; 95% CI, 6.64 to 18.25; P<0.001), with subsequent stabilization. In contrast, males demonstrated a steady increase throughout the study period. Conclusions: Breast cancer– and diabetes-associated mortality declined for more than a decade but reversed sharply after 2018, highlighting the vulnerability of patients with metabolic comorbidity. Persistently higher mortality among women and non-Hispanic Black individuals and the disproportionate burden in the Southern United States underscore important disparities. These findings emphasize the need for integrated oncologic and metabolic risk management strategies and renewed attention to chronic disease control in breast cancer survivorship.