Treating brain metastases in metastatic breast cancer: outcomes after stereotactic radiosurgery examined in a retrospective, single-center cohort analysis

Abstract

Introduction We examined the role of receptor profiles and other prognostic factors in survival outcomes after stereotactic radiosurgery (SRS) for brain metastases in breast cancer patients, to help improve selection of candidates for SRS. Material and methods We included 149 consecutive patients who received SRS between 2012 and 2019 at the University Hospital of Copenhagen, Rigshospitalet, Denmark. Overall survival (OS) following SRS was determined through the Kaplan–Meier method, while CNS progression-free survival (CNS-PFS) was determined through competing risk analysis. Prognostic factors for both OS and CNS-PFS were evaluated through uni- and multivariate Cox regression and Fine-Gray models, respectively. The proportional hazards assumptions were tested through Schoenfeld residuals, and non-proportionality was accounted for by the inclusion of time-dependent variables. Results Median OS was 14.8 months for the entire cohort and was as follows for the four receptor profiles: 33.3 months for ER+/HER2+ (ER: estrogen receptor, HER2: human epidermal growth factor receptor 2), 11.0 months for ER+/HER2−, 17.7 months for ER−/HER2+, and 5.3 months for ER−/HER2−. In the multivariate model, the ER−/HER2− receptor profile (hazard ratio (HR): 2.00, 95% confidence interval (CI): 1.09–3.67) and the presence of extracranial visceral metastases (HR: 2.90, 95% CI: 1.53–5.50) were associated with worse OS. The ER+/HER2+ receptor profile (HR: 0.43, 95% CI: 0.19–0.96) and 5+ lines of treatment (HR: 0.40, 95% CI: 0.20–0.82) were both associated with improved OS. For CNS-PFS, 5+ lines of treatment (sub-distributional hazard ratio (SHR): 2.88, 95% CI: 1.06–7.81) was associated with worse CNS-PFS, while extracranial visceral metastases (SHR: 0.54, 95% CI: 0.30–0.97) was associated with reduced risk of CNS progression – which is primarily due to patients with extracranial metastases dying before developing new CNS progression. Conclusion Extracranial visceral disease and the ER−/HER2− receptor profile were associated with poor survival outcomes following SRS.