Sociodemographic Disparities in First-Line Treatment and Outcome Patterns in Women With HR+/HER2– Metastatic Breast Cancer

Abstract Background: Various factors such as race/ethnicity, practice settings, socioeconomic status (SES), and geographic region influence cancer outcomes. We describe treatment patterns and outcomes among women with HR+/HER2– metastatic breast cancer treated in the United States based on these factors. Methods: A retrospective, observational cohort study was conducted using the Flatiron Health Research Database of de-identified electronic health records in women ≥18 years in the United States who received first-line treatment for HR+/HER2– metastatic breast cancer from 1/1/2015-2/28/2023. Real-world overall survival (rwOS) and time to next treatment or death (rwTTNTD) were assessed using Kaplan-Meier methods. Results: The analysis included 6,974 women, who were most commonly non-Hispanic White (64%), lived in the South (37%), and received treatment in community settings (83%). From 2015-2019, the early uptake period of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i), non-Hispanic White women were more likely to receive endocrine therapy (ET)+CDK4/6i versus non-Hispanic Black and Hispanic/Latino women; ET+CDK4/6i was less common in lower (Q1-Q3) versus higher (Q4-Q5) SES quintiles and in community versus academic settings. These differences were less pronounced from 2020-2023. Non-Hispanic White women had significantly longer rwOS versus non-Hispanic Black women, but shorter rwOS versus Hispanic/Latino women. RwOS was longer in academic versus community settings. No substantial differences in rwTTNTD were observed. Conclusions: We observed disparities in first-line treatment and outcomes among women with HR+/HER2– metastatic breast cancer during a time of changes to standard-of-care across racial/ethnic groups and practice settings. Impact: These findings emphasize the need for improved access to evidence-based therapies, particularly in underrepresented populations.