Influence of clinical, societal, and treatment variables on racial differences in ER-/PR- breast cancer survival.

BACKGROUND: African American (AA) women with breast cancer have persistently higher mortality compared to whites. We evaluated racial disparities in mortality among women with estrogen receptor (ER)/progesterone receptor (PR)-negative breast cancer.

METHODS: The study population included 542 women (45% AA) diagnosed with ER/PR-negative Stage I through III breast cancer treated at the Henry Ford Health System (HFHS) between 1996 and 2005. Linked datasets from HFHS, Metropolitan Detroit Cancer Surveillance System, and the U.S. Census Bureau were used to obtain demographic, socioeconomic, and clinical information. Economic deprivation was categorized using a previously validated deprivation index, which included 5 categories based on the quintile of census tract socioeconomic deprivation. Cox proportional hazards models were used to assess the relationship between race and mortality.

RESULTS: AA women were more likely to have larger tumors, have higher Charlson Comorbidity Indices (CCI), and to reside in economically deprived areas. In an unadjusted analysis, AA women demonstrated a significantly higher risk of death compared to whites [hazard ratio (HR) 1.47, 95% confidence interval (CI) 1.09-2.00]. Following adjustment for clinical factors (age, stage, CCI) and treatment (radiation and chemotherapy), AA race continued to have a significant impact on mortality (HR 1.51, CI 1.10-2.08 and HR 1.63, CI 1.20-2.21). Only after adjusting for deprivation was race no longer significant (HR 1.26, CI 0.84-1.87).

CONCLUSIONS: Social determinants of health play a large role in explaining racial disparities in breast cancer outcomes, especially among women with aggressive subtypes.