Patterns of de-novo metastasis and breast cancer-specific mortality by race and molecular subtype in the SEER population-based dataset

Purpose To examine patterns of de-novo metastases (mets) and association with breast cancer-specific mortality across subtypes and racial groups. Methods Non-Hispanic (NH) Black and NH-White patients ages 40 years and older with primary breast cancer (BC) between 2010 and 2015 were examined. Multilevel logistic regression and Cox proportional hazards models were used to assess (1) odds of de-novo mets to specific sites by subtype, and (2) association of subtype with risk of BC mortality among patients with de-novo mets by race. Results A total of 204,941 BC patients were included in analysis. The most common de-novo mets site was to the bone, and overall prevalence of de-novo mets was higher among NH-Black (6.4%) versus NH-White (4.1%) patients. The odds of de-novo mets to any site were lower for TNBC (OR 0.68, 95% CI 0.62-0.73) and HR+/HER2- (OR 0.50, 95% CI 0.47-0.53) subtypes, but higher for HR-/HER2+ (OR 1.16, 95% CI 1.06-1.28) relative to HR+/HER2+ . De-novo mets to the brain only was associated with the highest mortality risk across all subtypes, ranging from a 13-fold increase (hazard ratio 13.45, 95% CI 5.03-35.96) for HR-/HER2+ to a 39-fold increase (hazard ratio 39.04, 95% CI 26.2-58.14) for HR+/HER2-. Conclusion Site and fatality of de-novo mets vary by subtype and by race. This information may help improve risk stratification and post-diagnostic surveillance to ultimately reduce BC mortality.