Prognostic impact of metastatic pattern in stage IV breast cancer at initial diagnosis.

Purpose: To analyze the prognostic influence of metastatic pattern (MP) compared with other biologic and clinical factors in stage IV breast cancer at initial diagnosis (BCID) and evaluate factors associated with specific sites of metastases (SSM).

Methods: We evaluated women with stage IV BCID with known metastatic sites, reported to the Surveillance, Epidemiology and End Results program from 2010 to 2013. MP was categorized as bone-only, visceral, bone and visceral (BV), and other. Univariate and multivariate analyses determined the effects of each variable on overall survival (OS). Logistic regression examined factors associated with SSM.

Results: We included 9143 patients. Bone represented 37.5% of patients, visceral 21.9%, BV 28.8%, and other 11.9%. Median OS by MP was as follows: bone 38 months, visceral 21 months, BV 19 months, and other 33 months (P < 0.0001). Univariate analysis showed that higher number of metastatic sites had worse prognosis. In multivariate analysis, older age (hazard ratio 1.9), black race (hazard ratio 1.17), grade 3/4 tumors (hazard ratio 1.6), triple-negative (hazard ratio 2.24), BV MP (hazard ratio 2.07), and unmarried patients (hazard ratio 1.25) had significantly shorter OS. As compared with HR+/HER2- tumors, triple-negative and HR-/HER2+ had higher odds of brain, liver, lung, and other metastases. HR+/HER2+ had higher odds of liver metastases. All three subtypes had lower odds of bone metastases.

Conclusions: There were substantial differences in OS according to MP. Tumor subtypes have a clear influence among other factors on SSM. We identified several prognostic factors that could guide therapy selection in treatment naïve patients.