AbstractBackgroundDespite similar incidence rates among Black and White women, breast cancer mortality rates are 40% higher among Black women. More than half of the racial difference in breast cancer mortality can be attributed to triple negative breast cancer (TNBC), an aggressive subtype of invasive breast cancer that disproportionately affects Black women. Recent research has implicated neighborhood conditions in the etiology of TNBC. This study investigated the relationship between cumulative neighborhood‐level exposures and TNBC risk.MethodsThis single‐institution retrospective study was conducted on a cohort of 3316 breast cancer cases from New Castle County, Delaware (from 2012 to 2020), an area of the country with elevated TNBC rates. Cases were stratified into TNBC and “Non‐TNBC” diagnosis and geocoded by residential address. Neighborhood exposures included census tract‐level measures of unhealthy alcohol use, metabolic dysfunction, breastfeeding, and environmental hazards. An overall cumulative risk score was calculated based on tract‐level exposures.ResultsUnivariate analyses showed each tract‐level exposure was associated with greater TNBC odds. In multivariate analyses that controlled for patient‐level race and age, tract‐level exposures were not associated with TNBC odds. However, in a second multivariate model that included patient‐level variables and considered tract‐level risk factors as a cumulative exposure risk score, each one unit increase in cumulative exposure was significantly associated with a 10% increase in TNBC odds. Higher cumulative exposure risk scores were found in census tracts with relatively high proportions of Black residents.ConclusionsCumulative exposure to neighborhood‐level risk factors that disproportionately affect Black communities was associated with greater TNBC risk.