Abstract 3678: Drivers of racial, regional, and socioeconomic disparities in metastatic breast cancer mortality
Authors: Moubadder Leah , Collin Lindsay J. , Nash Rebecca , Switchenko Jeffrey , Miller-Kleinhenz Jasmine , Gogineni Keerthi , Ward Kevin C. , McCullough Lauren E. 
Published: June 2022

Abstract
Despite an overall decline in breast cancer (BC) mortality due to advancements in cancer therapy, mortality disparities by race, rurality, and socioeconomic status (SES) persist among women diagnosed with metastatic disease in the US. Women residing in high-poverty or rural areas or who are non-Hispanic Black (NHB) experience higher rates of BC mortality relative to their counterparts. Although mortality disparities among late-stage BC patients are well-documented, few studies have examined the drivers of these disparities, which are likely multifactorial. We sought to identify tumor, treatment, and patient characteristics that may contribute to differences in BC mortality by race, rurality, and SES among women diagnosed with a first primary stage IIIB - IV BC in Georgia.Using the Georgia Cancer Registry, we identified 3085 patients with an initial diagnosis of stage IIIB-IV primary BC between January 2013 and December 2017. Cox proportional hazards regression was used to calculate the hazard ratios (HRs) and 95% confidence intervals (CIs) to compare NHB vs. non-Hispanic White (NHW), rural vs. urban residents, and residents of low- vs. high-SES neighborhoods by tumor (stage, grade, ER status, and molecular subtype), treatment (surgery type, receipt of chemotherapy, radiation, hormonal, neoadjuvant, and immunotherapy), and patient (race, insurance, age group, marital status, region, SES) characteristics. Using an extension of the counterfactual framework, we estimated the mediating effects of subtype, stage, SES, rurality, and insurance on the association between race and BC mortality. Among the study population, 41% were NHB, 21% resided in rural counties, and 72% resided in low SES neighborhoods. Overall, we observed mortality disparities by race (HR=1.27, 95% CI: 1.13, 1.41) and rurality (HR=1.14, 95% CI: 1.00, 1.30), but not by SES (HR=1.04, 95% CI: 0.91, 1.19). In the stratified analyses, racial disparities were the most pronounced among women with HER2 overexpressing tumors (HR=2.30, 95% CI: 1.53, 3.45). Residing in a rural neighborhood was associated with increased mortality among uninsured women (HR=2.25, 95% CI: 1.31, 3.86) or receipt of breast-conserving surgery (HR=2.21, 95 CI%: 1.32, 3.71). The most pronounced socioeconomic disparities were among younger women (&lt;40 years: HR=1.46, 95% CI: 0.88, 2.42) and patients who received neoadjuvant therapy (HR=1.44, 95% CI: 1.01, 2.05). The mediation analysis demonstrated that 48% of the effect between race and BC mortality was mediated by subtype.There is considerable variation in racial, regional, and socioeconomic disparities in metastatic BC mortality by tumor, treatment, and patient characteristics. For each, we’ve identified patient groups where disparities are most pronounced. Understanding specific barriers within these patient groups will inform future interventions aimed at reducing disparities in metastatic BC mortality.
Citation Format: Leah Moubadder, Lindsay J. Collin, Rebecca Nash, Jeffrey Switchenko, Jasmine Miller-Kleinhenz, Keerthi Gogineni, Kevin C. Ward, Lauren E. McCullough. Drivers of racial, regional, and socioeconomic disparities in metastatic breast cancer mortality [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3678.