The Role of Residential Segregation in Treatment and Outcomes of Ductal Carcinoma In Situ of the Breast

Background: It remains unclear whether residential segregation impacts on clinical treatment and outcomes for ductal carcinoma in situ (DCIS), a nonobligate precursor to invasive breast cancer (IBC). Methods: This population-based retrospective cohort study included adult non-Hispanic White and Black women diagnosed with unilateral DCIS between January 1990 and December 2015, followed through December 2016, and identified from the Surveillance, Epidemiology, and End Results dataset. County-level racialized economic segregation was measured using the Index of Concentration at the Extremes. Multilevel logistic regression and Cox proportional hazards regression accounting for county-level clustering were used to estimate the ORs of local treatment and HRs of subsequent IBC and mortality. Results: Of 103,898 cases, mean age was 59.5 years, 12.5% were non-Hispanic Black, 87.5% were non-Hispanic White, 97.5% underwent surgery, 64.5% received radiotherapy following breast-conserving surgery (BCS), 7.1% developed IBC, and 18.6% died from all causes. Among women living in the least versus most privileged counties, we observed higher odds of receiving mastectomy [vs. BCS; OR = 1.51; 95% confidence interval (CI), 1.35–1.69; P_trend ≺ 0.001] and radiotherapy following BCS(OR = 1.27; 95% CI, 1.07–1.51; P_trend ≺ 0.01); the risk was higher in subsequent ipsilateral IBC (HR = 1.16; 95% CI, 1.02–1.32; P_trend = 0.04), not in breast cancer–specific mortality (HR = 1.04; 95% CI, 0.88–1.23; P_trend = 0.56). Conclusions: The results provide evidence for disparities in clinical treatment for DCIS and prognostic outcomes among women in racially and economically segregated counties. Impact: Our findings may inform geographically targeted multilevel interventions to reduce breast cancer burden and improve breast cancer care and equity.