Context: Reasons for the shorter survival of black breast cancer patients compared with their white counterparts are not completely understood.
Objective: To evaluate the role of comorbidity in this racial disparity among breast cancer patients.
Design, setting, and patients: Historical cohort from the Henry Ford Health System (a large comprehensive health system in Detroit, Mich) followed up for a median of 10 years. Patients (n = 906) included 264 black (29.1%) and 642 white (70.9%) women diagnosed as having breast cancer between 1985 and 1990. Detailed comorbidity data (268 comorbidities) and study data were abstracted from medical records and institutional, Surveillance, Epidemiology, and End Results, and Michigan State registries. Associations were analyzed with logistic and Cox regression.
Main outcome measures: Breast cancer recurrence/progression and survival to death from all, breast cancer, and competing (non-breast cancer) causes.
Results: Of blacks, 64 (24.9%) died of breast cancer and 95 (37.0%) died of competing causes. Comparable data for whites were 115 (18.3%) and 202 (32.1%). Blacks had worse all-cause survival (hazard ratio [HR], 1.34; 95% confidence interval [CI], 1.11-1.62), breast cancer-specific survival (HR, 1.47; 95% CI, 1.08-2.00), and competing-causes survival (HR, 1.27; 95% CI, 1.00-1.63). A total of 77 adverse comorbidities were associated with reduced survival. Adverse comorbidity count was associated with all-cause (adjusted HR, 1.29; 95% CI, 1.19-1.40) and competing-causes survival but was not associated with recurrence/progression or breast cancer-specific survival. At least 1 adverse comorbidity was observed in 221 (86.0%) blacks and 407 (65.7%) whites (odds ratio, 3.20; 95% CI, 2.17-4.72). Comparisons of unadjusted and comorbidity-adjusted HRs indicated that adverse comorbidity explained 49.1% of all-cause and 76.7% of competing-causes survival disparity. Diabetes and hypertension were particularly important in explaining disparity.
Conclusions: More black breast cancer patients die of competing causes than of breast cancer. Effective control of comorbidity in black breast cancer patients should help improve life expectancy and lead to a reduction in survival disparities.