Abstract B128: Rural-urban differences in breast cancer mortality: A national analysis integrating population-level trends and patient-level outcomes

Abstract

Breast cancer (BC) is the most diagnosed cancer and the second cause of cancer-related mortality among women in the United States. Approximately one-fifth of Americans live in rural areas, where barriers to screening, diagnosis, specialty care, and guideline-concordant treatment may contribute to worse outcomes. Although rural residence is associated with advanced presentation and poorer survival, the evolution and drivers of rural-urban BC mortality disparities remain unclear. This retrospective cohort study integrated data from the CDC WONDER Multiple Cause of Death database and patient-level data from the Surveillance, Epidemiology, and End Results (SEER) program. CDC WONDER analyses evaluated annual age-adjusted mortality rates (AAMR) for BC deaths (ICD-10 C50) from 1999-2020, using the 2013 NCHS urban-rural county classification. SEER analyses included women with invasive BC diagnosed from 2000-2020, classified using county-level Rural-Urban Continuum Codes, with BC-specific mortality as the primary outcome. Temporal trends, survival analyses, 2035 projections, Cox regression, mediation analysis, and Blinder-Oaxaca decomposition were performed. Among 688,165 SEER patients, 10.2% resided in rural counties. Compared with urban residents, rural women were older, predominantly non-Hispanic White, resided in lower-income counties, and more frequently presented with distant-stage disease or triple-negative BC; they received less radiotherapy and less neoadjuvant systemic therapy (all p<0.001). CDC WONDER analyses included 1,156,445 BC deaths (189,586 rural and 966,859 urban). Age-adjusted mortality declined over time in both populations, but rural mortality surpassed urban mortality in 2005. By 2020, rural mortality was higher (32.51 vs. 30.48 per 100,000, RR 1.07, p<0.001), with further widening projected by 2035 (difference +3.81 per 100,000, RR 1.13). Rural residence was associated with increased mortality in univariable analysis (HR=1.21, 95% CI 1.19-1.23) and remained independently associated after adjustment (aHR=1.03, 95% CI 1.01-1.06). Mediation analysis identified county-level income (45.3%), advanced stage at diagnosis (24.9%), radiation omission (11.4%), and chemotherapy omission (7.9%) as major contributors to excess mortality, while decomposition analysis confirmed socioeconomic disadvantage, disease presentation, and treatment differences as key contributors to the rural-urban mortality gap. No interaction was observed between geography and race, whereas socioeconomic context modified the association between rural residence and mortality, with higher mortality among rural patients in low-income counties (aHR=1.12, 95% CI 1.08-1.17). Rural populations experience persistently higher BC mortality, with disparities projected to widen. These differences likely reflect socioeconomic deprivation, later-stage presentation, and treatment disparities rather than geography alone. Improving early diagnosis and equitable access to high-quality oncology care is needed to reduce rural BC disparities. Nickolas Stabellini, Jennifer Cullen, Justin X. Moore, Arnethea L. Sutton, Siran M. Koroukian, Johnie Rose, Alberto J. Montero. Rural-urban differences in breast cancer mortality: A national analysis integrating population-level trends and patient-level outcomes [abstract]. In: Proceedings of the 19th AACR Conference on the Science of Cancer Health Disparities; 2026 Oct 18-21; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2026;35(10 Suppl):Abstract nr B128.