Abstract C072: Structural racism and race- and subtype-specific breast cancer incidence in California, 2006-2015
Authors: Michaels Elizabeth , Beyer Kirsten , Canchola Alison , Zhou Yuhong , Gomez Scarlett 
Published: August 2020

Background: Breast cancer is the most commonly diagnosed noncutaneous cancer and the second leading cause of death from cancer among women in the United States. Breast cancer is a heterogeneous disease and subtypes defined by hormone-receptor (HR) and HER2Neu status have distinct etiologic and prognostic profiles. African American women are more likely than White women to be diagnosed with HR-/HER2-, or triple-negative, breast cancer (TNBC), which is more aggressive and has a higher fatality rate than HR+ subtypes, including Luminal A. Determinants of racial disparities in breast cancer subtype are poorly understood. African Americans have historically been, and continue to be, subjected to institutionalized discrimination. Such discrimination, including housing discrimination, may contribute to breast cancer disparities, particularly, higher rates of TNBC among African American women. The aim of this study was to characterize the association between racial bias in mortgage lending and race- and subtype-specific breast cancer incidence rates in California.

Methods: We merged data from the California Cancer Registry on all women aged 20+ diagnosed with primary breast cancer between 2006-2015 with census tract characteristics where cases reside at time of diagnosis, including a new racial bias index, generated using data from the Home Mortgage Disclosure Act, 2007-2013. Racial bias was operationalized as the odds of a mortgage application denial for a Black applicant as compared to a White applicant, adjusting for individual sex, and the ratio of the loan amount to the applicant's gross annual income. We classified census tracts with an average Black-White mortgage denial OR&gt;2.5 as “high anti-Black bias.” Using Poisson regression with generalized estimating equations, we estimated the association between anti-Black bias and race-, age-, and subtype-specific breast cancer case counts, with population size as offset, and adjusting for census tract average age, socioeconomic status, racial composition, and residential stability.

Results: We identified n=104,716 cases of Luminal A breast cancer and n=14,238 cases of TNBC over the study period. Among White—but not African American—women, living in a census tract with high anti-Black bias was positively associated with incidence of Luminal A breast cancer (IRR=1.05, 95% CI=1.03, 1.07). This association was only slightly attenuated after adjusting for tract-level demographics (IRR=1.02, 95% CI=1.01, 1.04). No association was found between anti-Black bias and TNBC among either racial group (White IRR=1.00, 95% CI=0.96, 1.03; Black IRR=1.00, 95% CI=0.93, 1.01).

Conclusion: Among White women, living in communities with high levels of anti-Black housing discrimination may be associated with increased risk of Luminal A breast cancer. Future research into the psychosocial and/or material mechanisms underpinning this association is warranted.

Citation Format: Elizabeth Michaels, Kirsten Beyer, Alison Canchola, Yuhong Zhou, Scarlett Gomez. Structural racism and race- and subtype-specific breast cancer incidence in California, 2006-2015 [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 C072.