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.