Racial/ethnic differences in the outcomes of patients with metastatic breast cancer: contributions of demographic, socioeconomic, tumor and metastatic characteristics

PURPOSE: Population-based estimates of racial disparities in metastatic breast cancer are lacking. We quantified the contributions of demographic, socioeconomic, tumor, and metastatic characteristics to racial differences in metastatic breast cancer and characterized the most disproportional subgroup. METHODS: Patients diagnosed with metastatic breast cancer between 2010 and 2014 were identified using the Surveillance, Epidemiology, and End Results database. A multivariable Cox proportional hazards model was used to adjust each set of variables. The excess relative risk of cancer-specific and all-cause death in non-Hispanic black (NHB) versus non-Hispanic white women diagnosed with metastatic breast cancer was expressed as a percentage and was stratified by the age at diagnosis. RESULTS: We identified 13,066 female patients. NHB women exhibited substantially higher morbidity and mortality than women of other races/ethnicities. The greatest excess mortality risk for NHB women was observed in the young-onset group (18–49 years; hazard ratio: 1.57), followed by the middle-age group (50–64 years; hazard ratio: 1.42); the trend was not significant among the elderly group. Socioeconomic factors stably explained one-half of the excess risk, whereas the contribution of tumor characteristics obviously decreased with age (18–49 years, 40.7%; 50–64 years, 33.9%), and the metastatic pattern accounted for approximately one-tenth of the excess risk. Additionally, the disproportional death burden of NHB women persisted in less aggressive subgroups. CONCLUSIONS: By providing a comprehensive assessment of racial differences in the incidence and outcomes of patients with metastatic breast cancer, we urge the implementation of targeted preventive efforts in both the public health and clinical arenas. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s10549-018-4956-y) contains supplementary material, which is available to authorized users.