Optimal treatment of patients diagnosed with de novo metastatic breast cancer limited to the mediastinum or sternum has never been delineated. Herein, we sought to determine the efficacy of multimodality treatment, including metastasis-directed radiation therapy, in curing patients with this presentation.

This is a single-institution retrospective cohort study of patients with de novo metastatic breast cancer treated from 2005 to 2014, with a 50-month median follow-up for the primary cohort. The primary patient cohort had metastasis limited to the mediastinum/sternum treated with curative intent (n = 35). We also included a cohort of patients with stage IIIC disease treated with curative intent (n = 244). Additional groups included a mediastinal/sternal palliative cohort (treatment did not include metastasis-directed radiation therapy; n = 14) and all other patients with de novo stage IV disease (palliative cohort; n = 1185). The primary study outcomes included locoregional recurrence-free survival (LRRFS), recurrence-free survival (RFS), and overall survival (OS), which were calculated using the Kaplan-Meier method. Cox multivariable models compared survival outcomes across treatment cohorts adjusted for molecular subtype, age, and race.

For the mediastinal/sternal curative-intent cohort, 5-year LRRFS was 85%, RFS was 52%, and OS was 63%. After adjustment, there was no statistically significant difference in LRRFS (hazard ratio [HR], 0.39; 95% confidence interval [CI], 0.13-1.13; P = .08), RFS (HR, 0.87; 95% CI 0.50-1.49; P = .61), or OS (HR, 0.79; 95% CI 0.44-1.43; P = .44) between the stage IIIC cohort and the mediastinal/sternal curative-intent cohort (referent). In contrast, RFS was worse for the mediastinal/sternal palliative cohort (HR, 2.29; 95% CI 1.05-5.00; P = .04). OS was worst for the de novo stage IV palliative cohort (HR, 2.61; 95% CI 1.50-4.53; P < .001).

For select patients presenting with breast cancer metastatic to the sternum and/or mediastinum, curative-intent treatment with chemotherapy, surgery, and radiation yields outcomes similar to those of stage IIIC disease and superior to de novo stage IV breast cancer treated with palliative intent.