Abstract B085: Associations of African genetic ancestry and neighborhood social environment with cancer-specific mortality in the Multiethnic Cohort
Authors: Iyer Hari S. , Gomez Scarlett L. , Opara Chidinma , Zeinomar Nur , LeMarchand Loic , Haiman Christopher , Wilkens Lynne , Shariff-Marco Salma , Conti David V. , Cheng Iona , Rebbeck Timothy R. 
Published: December 2023

Abstract
Importance: Evaluating contributions of both genetic and social environmental factors to cancer mortality in Black populations is necessary for prioritizing interventions to reduce racial disparities and inequities. We examined multilevel associations of African genetic ancestry (AGA) and the neighborhood social environment with cancer-specific mortality in Black participants in the Multiethnic Cohort Study. Methods: From 1993 through 1996, participants who self-identified as Black as their primary race, and were aged 45-75 years residing in Los Angeles County completed baseline demographic, clinical, and lifestyle questionnaires to enroll into the Multiethnic Cohort Study. Residential addresses were collected and geocoded to the nearest parcel, and deaths were ascertained over follow-up through December 31, 2019. For this prospective study, we analyzed data on participants with genetic ancestry data and geocoded addresses (n=10,722). Global African and European genetic ancestry was estimated using approximately 21,000 ancestry specific markers, from which AGA was estimated for each participant against the 1000 Genomes referent panel (K=2). A neighborhood socioeconomic status (nSES) index and the Index of Concentration at Extremes (ICE) capturing spatial social polarization based on income and racial composition were computed from the 1990 decennial Census and linked to residential census tracts at baseline. Cancer-specific mortality was assigned based on ICD-09 and ICD-10 codes. We estimated subdistribution hazard ratios (SHR) from Fine-Gray competing risks models adjusted for birth cohort, sex, smoking, marital status, education, body mass index (BMI), BMI at age 21, history of hypertension, physical activity, diet quality, and nSES or African ancestry. Results: There were 1,715 cancer deaths over 226,327 person-years of follow-up. Mean age was 61.1 (SD=8.9) years, mean AGA was 76% (SD=15%). Most participants identified as Black (94%) while others reported mixed (White, Hispanic, or Asian) heritage. Higher AGA was associated with lower individual education and nSES (Both P&lt;0.001). AGA was not associated with cancer mortality (SHR for 10% increase: 1.02, 95% CI: 0.99-1.06). Comparing quintile 5 to 1, there were inverse but not statistically significant associations of nSES (SHR: 0.88, 95% CI: 0.71-1.09, P trend=0.34), ICE Income (SHR: 0.92, 95% CI: 0.73-1.16, P trend=0.36), and racialized income ICE (SHR: 0.81, 0.58-1.13, P trend=0.033) with cancer mortality. Associations of AGA and nSES with cancer mortality did not vary across strata of the other exposure. Conclusions and Relevance: In this large prospective study of Black participants, after accounting for sociodemographic, lifestyle, and comorbidity-related factors, there were few associations between either genetic factors or social environment with cancer mortality. Additional studies in cohorts of Black adults residing in other geographic contexts, with additional measures of social determinants of health such as health care access, are needed to further evaluate these findings.
Citation Format: Hari S. Iyer, Scarlett L. Gomez, Chidinma Opara, Nur Zeinomar, Loic LeMarchand, Christopher Haiman, Lynne Wilkens, Salma Shariff-Marco, David V. Conti, Iona Cheng, Timothy R. Rebbeck. Associations of African genetic ancestry and neighborhood social environment with cancer-specific mortality in the Multiethnic Cohort [abstract]. In: Proceedings of the 16th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2023 Sep 29-Oct 2;Orlando, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2023;32(12 Suppl):Abstract nr B085.