Abstract 775: Racial and ethnic differences in the impacts of rurality on cancer-specific survival among women with de novo metastatic breast cancer
Authors: Smart Mary H. , Huang Hsiao-Ching , Zolekar Ashwini , Deng Huiwen , Hubbard Colin C. , Hoskins Kent , Ko Naomi Y. , Calip Gregory S. 
Published: July 2021

Background: The interaction of racial/ethnic and geographic disparities in determining breast cancer (BC) outcomes is not fully understood. Our purpose was to examine racial and ethnic differences in and the impact of rurality on breast cancer specific mortality among women diagnosed with metastatic BC in the U.S.

Methods: We conducted a large, population-based cohort study using the Surveillance, Epidemiology, and End Results rurality database of women ages 18+ years diagnosed with de novo metastatic BC between 2000 and 2015. Our main exposure of interest was U.S. Department of Agriculture Rural Urban Commuting Area categories, and our outcome of interest was BC-specific mortality. We collected information on demographic and clinical characteristics, including molecular subtypes, treatment, survival and cause of death. We determined associations between rurality and BC-specific mortality in Fine and Gray regression models and calculated subdistribution hazard ratios (SHR) and 95% confidence intervals (CI) accounting for competing risks of death and with adjustment for age, year of diagnosis, hormone receptor (HR) status, treatment, marital status and insurance status. We calculated overall and race specific SHR estimates to understand racial/ethnic differences in impacts of rurality on BC mortality and performed stratified analyses by HR status.

Results: From an overall cohort of 31,991 de novo metastatic BC patients with a median age of 60 years, there were 29,069 patients in urban commuting areas vs. 2,922 in rural areas. Compared to rural areas, lower proportions of non-Hispanic white (65% vs. 81%) and Asian/Pacific islander (0.3% vs. 0.9%) patients, and higher proportions of Black (17% vs. 10%) and Hispanic (10% vs. 5%) patients lived in urban areas. Metastatic BC patients living in urban commuting areas were more likely to receive surgery compared to rural (56% vs. 48%) and have a positive joint HR status (12% vs. 9%), but were similar with respect to radiation (33% vs. 33%) and chemotherapy (53% vs. 51%). Overall, women living in rural areas had a modestly higher risk of BC-specific mortality (adjusted SHR 1.01, 95% CI 1.00-1.02); however, the impact of rurality differed by race/ethnicity and HR status. Among white women with HR-positive metastatic BC, rurality was associated with an increased risk of BC mortality (SHR 1.09, 95% CI 1.03-1.15). Among Black women with HR-negative metastatic BC, we observed the greatest increased risk of BC mortality associated with rurality (SHR 1.27, 95% CI 1.01-1.59).

Conclusion: BC-specific survival among women with de novo metastatic disease differs by race/ethnicity and geography with the greatest adverse impacts of rurality affecting Black women with HR-negative BC.

Citation Format: Mary H. Smart, Hsiao-Ching Huang, Ashwini Zolekar, Huiwen Deng, Colin C. Hubbard, Kent Hoskins, Naomi Y. Ko, Gregory S. Calip. Racial and ethnic differences in the impacts of rurality on cancer-specific survival among women with de novo metastatic breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 775.