Disparities in Disease Presentation and Treatment Initiation for De Novo Metastatic Breast Cancer

Importance: In the US, patients from minoritized racial and ethnic groups generally receive diagnoses at later stages of breast cancer, face care barriers, and experience worse outcomes, despite advances in screening and treatment. There remain limited data on disparities in presentation and treatment initiation timing for de novo metastatic breast cancer (dnMBC) nationally. Objective: To examine patterns of disease presentation and treatment initiation for dnMBC by race and ethnicity. Design, setting, and participants: This study is a retrospective cross-sectional analysis of the 2010 to 2022 National Cancer Database evaluating presentation and treatment differences in 3 main subtypes: hormone receptor (HR)-positive and epidermal growth factor receptor 2 (ERBB2)-negative, ERBB2-positive, and triple-negative breast cancer (TNBC). Data were analyzed from March to September 2025. Exposure: Diagnosis of dnMBC. Main outcomes and measures: Metastatic sites were categorized as brain, bone only, and visceral (ie, liver and/or lung). Treatment modalities were categorized as chemotherapy, endocrine therapy, ERBB2-directed therapy, immunotherapy, and radiotherapy. Treatment initiation timing was defined as days between diagnosis and treatment start, modeled using multiple linear regression. Results: Among 117 743 female patients with dnMBC (mean [SD] age, 62.0 [14.1] years; 4271 [3.7%] Asian or Pacific Islander, 20 153 [17.3%] Black, 7785 [6.7%] Hispanic, and 83 337 [71.3%] White), 72 874 (61.9%) had HR-positive-ERBB2-negative disease, 27 972 (23.8%) had ERBB2-positive disease, and 16 897 (14.3%) had TNBC. In the HR-positive-ERBB2-negative cohort, higher proportions of Black and Hispanic patients presented with brain metastases; White patients more commonly presented with bone-only metastases. Compared with White patients, Black patients experienced longer days to endocrine therapy initiation (β, 6.6; 95% CI, 4.5-8.8), chemotherapy (β, 3.6; 95% CI, 1.4-5.8), and radiotherapy (β, 11.3; 95% CI, 5.9-16.7). Similar delays occurred among Asian or Pacific Islander and Hispanic patients. In the ERBB2-positive cohort, bone-only metastases were more common among White patients. Black patients experienced longer ERBB2-directed therapy initiation timing (β, 5.7; 95% CI, 2.9-8.6) and chemotherapy (β, 5.1; 95% CI, 0.1-10.1) than White patients; Hispanic patients also experienced delays. Among patients with TNBC, bone-only metastases were higher among Asian or Pacific Islander patients, brain metastases were higher among White patients, and visceral metastases were higher among Black patients. Compared with White patients, Black (β, 7.8; 95% CI, 0.6-15.1) and Hispanic (β, 16.6; 95% CI, 6.0-27.2) patients experienced longer times to immunotherapy initiation, although the difference was no longer significant after socioeconomic covariate adjustment. Living in lower-income and lower-education areas and use of public or lack of insurance were associated with heterogeneous delays across subtypes and treatment modalities. Conclusions and relevance: This cross-sectional study of patients with dnMBC found racial and ethnic disparities in disease presentation and inequities in timely treatment for dnMBC across subtypes, emphasizing the need for tailored interventions to improve care delivery and outcomes.