Breast cancer subtypes and the risk of distant metastasis at initial diagnosis: a population-based study.

BACKGROUND: It was unclear whether breast cancer subtypes are associated with the risk of site-specific metastases. This study aimed to evaluate the relationship between molecular subtypes and distant metastatic sites and their prognostic significance.

METHODS: We identified 295,213 patients with invasive breast cancer from 2010 to 2014 using the Surveillance, Epidemiology and End Results database. Subtypes were classified into four categories: hormone receptor (HR+ )/human epidermal growth factor receptor 2 (HER2- ), HR+ /HER2+ , HR- /HER2+ , and triple-negative (HR- /HER2- ). Logistic regression was used to assess the association between metastasis location and subtypes. Multivariate Cox models were used to estimate the overall survival (OS) of related factors.

RESULTS: According to our study, 3.28%, 1.52%, 1.20%, and 0.35% of newly diagnosed breast cancers presented bone, lung, liver, and brain metastases at diagnosis, respectively. Both metastatic sites and subtypes significantly affected the OS after metastasis. In multivariate analysis, HR+ /HER2+ subtype (OR as compared with HR+ /HER2- subtype, 1.30 [95% CI, 1.22-1.39]) significantly correlated with elevated bone metastasis risk, whereas HR- /HER2+ did not. Both HER2+ subtypes (HR+ /HER2+ and HR- /HER2+ ) were significantly associated with higher rates of liver, brain, and lung metastases, while the highest OR was observed in liver metastases. Triple-negative tumors had a higher rate of brain (OR, 1.95 [95% CI, 1.61-2.35]), liver (OR, 1.35 [95% CI, 1.20-1.51]), and lung metastases (OR, 1.34 [95% CI, 1.21-1.47]), but a significantly lower rate of bone metastases (OR, 0.64 [95% CI, 0.59-0.69]) than HR+ /HER2-tumors.

CONCLUSIONS: Breast cancer subtypes are associated with different metastatic patterns and confer different prognostic impacts. Molecular subtypes can identify patients at increased risk of site-specific metastases.