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

Abstract

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 ≥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. Cancer 2008. © 2007 American Cancer Society. Breast cancer is the most common cancer and the second leading cause of cancer death among women in the U.S.1 Although there has been an overall reduction in breast cancer mortality rates in the U.S. since the 1990s, most of this benefit has been experienced by white women.2 African American (AA) and Hispanic (H) women remain more likely to be diagnosed with poor prognostic breast cancers (ie, late stage, large size, lymph node-positive, estrogen receptor-negative) with AA women experiencing worse survival than white women, a disparity that has increased rather than decreased over time.3 In contrast, Asian/Pacific Island (A/PI) women tend to have better prognostic breast cancers (ie, early stage, small size, lymph node-negative, estrogen receptor-positive) and better survival than white women.4 The reasons for the persistence of these racial and ethnic disparities have been difficult to disentangle. Possible explanations include differences in screening mammography leading to differences in the stage and size of tumors at diagnosis,5, 6 tumor biology, inadequate receipt of appropriate breast cancer treatment,5 and underlying patient comorbidities and socioeconomic factors.7–11 Several studies have used Surveillance, Epidemiology, and End Results (SEER) program information to explore these issues.3, 4, 12–18 Although SEER data include valuable regional information on a large, geographically diverse population, it lacks detailed information concerning screening mammography use and underlying comorbidities that may impact survival.19 This study aims to overcome these problems by using the combined SEER-Medicare dataset to explore the contribution of screening, tumor characteristics, biology, treatment, comorbidities, and demographics to race/ethnicity (R/E) differences in breast cancer survival for elderly women.