Census tract-level income inequality and colorectal cancer survival

Background: Income inequality has been associated with greater mortality and lower life expectancy in many ecologic studies, particularly at the national level. At the neighborhood level, the influence of income inequality on individual health is less clear. Colorectal cancer (CRC) is the second leading cause of cancer death in the United States. Recent studies suggest that neighborhood social and built environments are associated with outcomes across the CRC continuum, including screening, risk, and survival. Few studies of neighborhood factors have examined income inequality in relation to CRC survival. Methods: We examined the association of census tract-level income inequality with survival among women who participated in the Women9s Health Initiative (WHI) and were diagnosed with incident invasive CRC between 1994-2014 (N=2,595). Based on geocoded residence at diagnosis and year of diagnosis, we linked each participant to census tract-level data from the US Census and American Community Survey (ACS). Within each tract, income inequality was assessed using the ratio of the 95th and 20th percentiles for household income. Quartiles for 95/20 ratio were constructed from the distribution of 95/20 ratios across all U.S. census tracts with more than 50 households. We used Cox proportional hazards regression models to estimate hazard ratios (HR) and 95% confidence intervals (CI) for overall and disease-specific survival. Models were adjusted for age at diagnosis, year of diagnosis, individual household income, and tract-level percent of households in poverty; subsequent models also adjusted for tumor stage at diagnosis. To explore whether the relationship between income inequality and survival differed by individual or tract-level sociodemographic characteristics, we conducted analyses stratified by race/ethnicity, individual household income, and tract-level poverty. Results: Compared to women residing in low-income-inequality census tracts, women living in tracts with the highest income inequality had modestly poorer overall survival (HR=1.24, 95% CI: 1.01-1.51, comparing highest and lowest quartiles). However, this association was not significant after adjustment for stage at diagnosis. No associations were detected for disease-specific survival. The associations between income inequality and overall or disease-specific survival were not modified by tract-level poverty, individual household income, or race/ethnicity. Conclusion: There was no association between census tract-level income inequality and CRC survival in our study. Our results suggest that the association may be confounded or even mediated by disparities in stage at diagnosis. Citation Format: Kelsey A. Chun, Jamaica R. Robinson, Candace H. Kroenke, Dorothy S. Lane, Giselle Corbie-Smith, Theresa Hastert, Shawnita Sealy-Jefferson, Manali I. Patel, Kathy Pan, Shirley A.A. Beresford, Polly A. Newcomb. Census tract-level income inequality and colorectal cancer survival [abstract]. In: Proceedings of the Eleventh AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2018 Nov 2-5; New Orleans, LA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl):Abstract nr C068.