Metrics for monitoring cancer inequities: residential segregation, the Index of Concentration at the Extremes (ICE), and breast cancer estrogen receptor status (USA, 1992-2012)

Purpose: To address the paucity of evidence on residential segregation and cancer, we explored their relationship using a new metric: the Index of Concentration at the Extremes (ICE). We focused on breast cancer estrogen receptor (ER) status, a biomarker associated with survival and, etiologically, with social and economic privilege.

Methods: We obtained data from the 13 registry group of US Surveillance, Epidemiology, and End Results (SEER) program for 1992-2012 on all women aged 25-84 who were diagnosed with primary invasive breast cancer (n = 516,382). We appended to each case's record her annual county median household income quintile and the quintile for her annual county value for ICE measures for income (≤20th vs. ≥80th household income quintile), race/ethnicity (black vs. white), and income plus race/ethnicity (low-income black vs. high-income white). The odds of being ER+ versus ER- were estimated in relation to the county-level income and ICE measures, adjusting for relevant covariates.

Results: Women in the most privileged versus deprived county quintile for household income and for all three ICE measures had a 1.1- to 1.3-fold increased odds (95 % confidence intervals excluding 1) of having an ER+ tumor. These results were robust to adjustment for age at diagnosis, cancer registry, tumor characteristics (tumor stage, size, histology, grade), and race/ethnicity.

Conclusion: A focus on segregation offers news possibilities for understanding how inequitable group relations contribute to cancer inequities. The utility of employing the ICE for monitoring cancer inequities should be investigated in relation to other cancer outcomes.