Measures Matter: The Local Exposure/Isolation (LEx/Is) Metrics and Relationships between Local-Level Segregation and Breast Cancer Survival

Abstract

Background: The Black-to-White disparity in breast cancer survival is increasing, and racial residential segregation is a potential driver for this trend. However, study findings have been mixed, and no study has comprehensively compared the effectiveness of different local-level segregation metrics in explaining cancer survival.Methods: We proposed a set of new local segregation metrics named local exposure and isolation (LEx/Is) and compared our new local isolation metric with two related metrics, the location quotient (LQ) and the index of concentration at extremes (ICE), across the 102 largest U.S. metropolitan areas. Then, using case data from the Milwaukee, WI, metropolitan area, we used proportional hazards models to explore associations between segregation and breast cancer survival.Results: Across the 102 metropolitan areas, the new local isolation metric was less skewed than the LQ or ICE. Across all races, Hispanic isolation was associated with poorer all-cause survival, and Hispanic LQ and Hispanic-White ICE were found to be associated with poorer survival for both breast cancer-specific and all-cause mortality. For Black patients, Black LQ was associated with lower all-cause mortality and Black local isolation was associated with reduced all-cause and breast cancer-specific mortality. ICE was found to suffer from high multicollinearity.Conclusions: Local segregation is associated with breast cancer survival, but associations varied based on patient race and metric employed.Impact: We highlight how selection of a segregation measure can alter study findings. These relationships need to be validated in other geographic areas. Cancer Epidemiol Biomarkers Prev; 26(4); 516-24. ©2017 AACRSee all the articles in this CEBP Focus section, "Geospatial Approaches to Cancer Control and Population Sciences."

Figure 1

Comparisons of the distribution of ZCTA level Black segregation indices in the 102 largest MSAs in the US (left column), the 15 most Black-White segregated of those MSAs (middle column), and the 15 least segregated (right column)

Figure 2

TOP: Maps of Milwaukee-Waukesha-West Allis, WI MSA. TOP LEFT: Dot map of racial distribution in study area by ZCTA. TOP RIGHT: Percent households below poverty line in study area by ZCTA. BOTTOM: Jittered distribution of patients by race for each segregation index. Top row is Black segregation indices, bottom row is Hispanic segregation indices. Columns from left to right are: local isolation, LQ, ICE (uncontrolled for income), ICE (controlled for income). Boxes correspond to the 1^st to 3^rd quartiles of each race’s distribution. Whiskers extend to 1.5-times the inter-quartile range.