Site of metastasis and breast cancer mortality: a Danish nationwide registry-based cohort study.

Survival among patients with metastatic breast cancer may vary according to the site of metastasis and receptor status. We used Danish nationwide medical registries to establish a cohort of patients with metastatic breast cancer (870 with de novo metastatic disease and 3518 with recurrent disease with distant metastasis) diagnosed during 1997-2011. We examined 1-year and >1 to 5-year mortality associated with first site of metastasis and receptor expression status of the primary tumor. Cox proportional regression was used to compute confounder-adjusted mortality rate ratios (MRRs) associated with site of metastasis, stratified by receptor status. Overall 1-year and >1 to 5-year mortality risks were 36 and 69 %, respectively. Risk of death within 1 year was highest for brain-only (62 %) and liver-only (43 %) involvement and nearly the same for patients with lung-only (32 %), bone-only (32 %) involvement, and other/combination of sites (34 %). Using bone-only metastasis as reference, women with brain-only metastasis had more than two-fold increased risk of dying. The adjusted MRR for women with liver-only metastasis also was increased, though less pronounced. Patients with lung-only [adjusted MRR 0.9 (95 % confidence interval (CI) 0.8, 1.1)] or other metastases [adjusted MRR 1.0 (95 % CI 0.9, 1.2)] had similar mortality as patients with bone-only metastasis. Positive hormonal receptor status was a favorable prognostic factor. Metastatic breast cancer has a serious prognosis. Patients with brain-only metastasis had the highest mortality. Positive hormonal receptor status on the primary tumor was a favorable prognostic factor for all metastatic sites.