Zip-Code Level Disadvantage as a Predictor of Metastatic Breast Cancer at Diagnosis and Delayed Treatment Initiation

Metastatic breast cancer remains a significant public health issue, associated with worse outcomes and limited treatment options. While tumor biology influences disease progression, social and geographic disparities also contribute to late-stage diagnosis. The Distressed Communities Index (DCI), a zip-code level measure of economic hardship, captures structural disadvantage more comprehensively than traditional socioeconomic indicators. This study evaluates whether higher DCI scores are associated with metastatic stage and treatment delays, independent of clinical and demographic factors.

We conducted a retrospective cohort study of women aged ≥ 18 years diagnosed or treated for in situ (DCIS) and invasive breast cancer (2018-2022) at a comprehensive cancer center. Zip codes were linked to DCI scores. Multinomial logistic regression, adjusted for age, race, ethnicity, insurance status, tumor subtype, and clinical palpable mass, assessed the association between DCI and cancer stage. Analysis of covariance compared time with treatment across DCI groups.

Among 2024 women (38% Black, 39% Hispanic), 76.8% resided in high DCI areas. High DCI was associated with twice the likelihood of metastatic disease at diagnosis compared with localized stage (ref: low DCI, aOR 2.16, 95% CI 2.00-2.34, p < 0.001) after adjustment. High DCI patients also experienced longer time to treatment initiation, including adjuvant chemotherapy (119 versus 137 days, p = 0.024), radiation (103 versus 133 days, p < 0.001), and surgery (71.2 versus 87.4 days, p < 0.001), after adjustment for stage.

Leveraging DCI may help identify high-risk zip codes and guide targeted screening to reduce disparities in outcomes.