Gamma Knife Radiosurgery for Brain Metastases from Breast Cancer

Objective : The authors conducted a retrospective cohort study to determine prognostic factors and treatment outcomes of brain metastases (BM) from breast cancer (BC) after Gamma Knife radiosurgery (GKS). Methods : Pathologic and clinical features, and outcomes were analyzed in a cohort of 62 patients with BM from BC treated by GKS. The Kaplan- Meier method, the log-rank test, and Cox's proportional hazards model were used to assess prognostic factors. Results : Median survival after GKS was 73.0 weeks (95% confidence interval, 46.0-100.1). HER2+ [hazard ratio (HR) 0.441; p=0.045], Karnofsky performance scale (KPS) ${\geq}70$ (RR 0.416; p=0.050) and systemic chemotherapy after GKS (RR 0.282; p=0.001) were found to be a favorable prognostic factor of overall survival. Actuarial local control (LC) rate were $89.5{\pm}4.5%$ and $70.5{\pm}6.9%$ at 6 and 12 months after GKS, respectively. No prognostic factors were found to affect LC rate. Uni- and multivariate analysis revealed that the distant control (DC) rate was higher in patients with; a small number (${\leq}3$) of metastasis (HR 0.300; p=0.045), no known extracranial metastasis (p=0.013, log-rank test), or the HER2+ subtype (HR 0.267; p=0.027). Additional whole brain radiation therapy and metastasis volume were not found to be significantly associated with LC, DC, or overall survival. Conclusion : The treatment outcomes of patients with newly diagnosed BM from BC treated with GKS could be affected primarily by intrinsic subtype, KPS, and systemic chemotherapy. Therapeutic strategy and prognosis scoring system should be individualized based on considerations of intrinsic subtype in addition to traditionally known parameters related to stereotactic radiosurgery.