Racial and ethnic differences in breast cancer survival: how much is explained by screening, tumor severity, biology, treatment, comorbidities, and demographics?

Background: The reasons for race/ethnicity (R/E) differences in breast cancer survival have been difficult to disentangle.

Methods: Surveillance, Epidemiology, and End Results (SEER)-Medicare data were used to identify 41,020 women aged > or =68 years with incident breast cancer between 1994-1999 including African American (2479), Hispanic (1172), Asian/Pacific Island (1086), and white women (35,878). A Cox proportional hazards model assessed overall and stage-specific (0/I, II/III, and IV) R/E differences in breast cancer survival after adjusting for mammography screening, tumor characteristics at diagnosis, biologic markers, treatment, comorbidity, and demographics.

Results: African American women had worse survival than white women, although controlling for predictor variables reduced this difference among all stage breast cancer (hazards ratio [HR], 1.08; 95% confidence interval [95% CI], 0.97-1.20). Adjustment for predictors reduced, but did not eliminate, disparities in the analysis limited to women diagnosed with stage II/III disease (HR, 1.30; 95% CI, 1.10-1.54). Screening mammography, tumor characteristics at diagnosis, biologic markers, and treatment each produced a similar reduction in HRs for women with stage II/III cancers. Asian and Pacific Island women had better survival than white women before and after accounting for all predictors (adjusted all stages HR, 0.61 [95% CI, 0.47-0.79]; adjusted stage II/III HR, 0.61 [95% CI, 0.47-0.79]). Hispanic women had better survival than white women in all and stage II/III analysis (all stage HR, 0.88; 95% CI, 0.75-1.04) and stage II/III analysis (HR, 0.88; 95% CI, 0.75-1.04), although these findings did not reach statistical significance. There was no significant difference in survival by R/E noted among women diagnosed with stage IV disease.

Conclusions: Predictor variables contribute to, but do not fully explain, R/E differences in breast cancer survival for elderly American women. Future analyses should further investigate the role of biology, demographics, and disparities in quality of care.