Racial and Ethnic Differences in Breast Cancer Survival: Mediating Effect of Tumor Characteristics and Sociodemographic and Treatment Factors.

Purpose: To evaluate the relationship between race/ethnicity and breast cancer-specific survival according to subtype and explore mediating factors.
Patients and Methods: Participants were women presenting with stage I to III breast cancer between January 2000 and December 2007 at National Comprehensive Cancer Network centers with survival follow-up through December 2009. Cox proportional hazards regression was used to compare breast cancer-specific survival among Asians (n = 533), Hispanics (n = 1,122), and blacks (n = 1,345) with that among whites (n = 14,268), overall and stratified by subtype (luminal A like, luminal B like, human epidermal growth factor receptor 2 type, and triple negative). Model estimates were used to derive mediation proportion and 95% CI for selected risk factors.
Results: In multivariable adjusted models, overall, blacks had 21% higher risk of breast cancer-specific death (hazard ratio [HR], 1.21; 95% CI, 1.00 to 1.45). For estrogen receptor-positive tumors, black and white survival differences were greatest within 2 years of diagnosis (years 0 to 2: HR, 2.65; 95% CI, 1.34 to 5.24; year 2 to end of follow-up: HR, 1.50; 95% CI, 1.12 to 2.00). Blacks were 76% and 56% more likely to die as a result of luminal A-like and luminal B-like tumors, respectively. No disparities were observed for triple-negative or human epidermal growth factor receptor 2-type tumors. Asians and Hispanics were less likely to die as a result of breast cancer compared with whites (Asians: HR, 0.56; 95% CI, 0.37 to 0.85; Hispanics: HR, 0.74; 95% CI, 0.58 to 0.95). For blacks, tumor characteristics and stage at diagnosis were significant disparity mediators. Body mass index was an important mediator for blacks and Asians.
Conclusion: Racial disparities in breast cancer survival vary by tumor subtype. Interventions are needed to reduce disparities, particularly in the first 2 years after diagnosis among black women with estrogen receptor-positive tumors.
(© 2015 by American Society of Clinical Oncology.)