Background: Higher breast cancer mortality rates for African- American than non-Hispanic Whitewomen are well documented; however, it remains uncertain if this disparity occurs in disease subgroups defined by tumor molecular markers and stage at diagnosis. We examined racial differences in outcome according to subtype and stage in a diverse, population-based series of 103,498 patients. Methods: We obtained data for all invasive breast cancers diagnosed between January 1, 2005, and December 31, 2012, and followed through December 31, 2012, among 93,760 non- Hispanic White and 9,738 African-American women in California. Molecular subtypes were categorized according to tumor expression of hormone receptor (HR, based on estrogen and progesterone receptors) and human epidermal growth factor receptor 2 (HER2). Cox proportional hazards models were used to calculate relative hazard (RH) and 95% confidence intervals (CI) for breast cancer-specific mortality. Results: After adjustment for patient, tumor, and treatment characteristics, outcomes were comparable by race for stage I or IV cancer regardless of subtype, and HR+/HER2+ or HR/HER2 cancer regardless of stage. We found substantially higher hazards of breast cancer death among African-American women with stage II/III HR/HER2 (RH, 1.31; 95% CI, 1.03-1.65; and RH, 1.39; 95% CI, 1.10-1.75, respectively) and stage III triple-negative cancers relative to Whites. Conclusions: There are substantial racial/ethnic disparities among patients with stages II/III HR/HER2 and stage III triple-negative breast cancers but not for other subtype and stage. Impact: These data provide insights to assess barriers to targeted treatment (e.g., trastuzumab or endocrine therapy) of particular subtypes of breast cancer among African-American patients.
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