Associations Between Neighborhood-Level Income and Triple-Negative Breast Cancer in a Majority-Minority Population

Background: Previous studies on disparities in triple-negative breast cancer (TNBC) focus on race/ethnicity, with few exploring the impact of contextual factors such as neighborhood-level income. This study evaluates the effect of neighborhood-level income on disparities in TNBC among a racially and ethnically diverse cohort, after accounting for granular individual-level risk factors of TNBC.

Patients and methods: Patients with stage I-IV breast cancer from 2005 to 2017 were identified from our local tumor registry. The primary outcome was diagnosis of TNBC. Using 5-years estimates from the American Community Survey, we obtained median household income for each census tract which was categorized into quartiles. Mixed effects logistic regression was conducted and stratified by race and ethnicity, controlling for individual-level sociodemographic, comorbidities, and tumor characteristics.

Results: Among 5377 breast cancer registry patients, 16.5% were diagnosed with TNBC. The majority were Hispanic (50.1%) followed by non-Hispanic Black (NHB) (28.0%). After controlling for individual-level covariables including race and ethnicity, comorbidities, and tumor characteristics, women from low-income neighborhoods had increased odds of TNBC compared with other breast cancer subtypes, compared with those in high-income neighborhoods [odds ratio (OR) 1.33; 95% confidence interval (CI) 1.04, 1.70, p < 0.001]. In stratified analyses, NHB patients from low-income neighborhoods had two times the odds of TNBC diagnosis compared with those from high-income neighborhoods (OR 2.11; 95% CI 1.02, 4.37).

Conclusion: We found that living in a low-income neighborhood is associated with an increased odds of TNBC independent of granular individual-level TNBC risk factors, particularly NHB race. More striking, NHB living in low-income neighborhoods had increased odds of TNBC compared with NHB living in high-income neighborhoods. Our results suggest potential unaccounted gene-environment and/or social (api)genomic interactions between neighborhood-level income and TNBC subtype development.