Importance of extracranial disease status and tumor subtype for patients undergoing radiosurgery for breast cancer brain metastases

Purpose: In this retrospective study, we report on outcomes and prognostic factors for patients treated with stereotactic radiosurgery (SRS) for breast cancer brain metastases. Methods and Materials: We identified 132 consecutive patients with breast cancer who were treated with SRS for brain metastases from January 2000 through June 2010. We retrospectively reviewed records of the 51 patients with adequate follow-up data who received SRS as part of the initial management of their brain metastases. Overall survival (OS) and time to central nervous system (CNS) progression from the date of SRS were calculated using the Kaplan-Meier method. Prognostic factors were evaluated using the Cox proportional hazards model. Results: Triple negative subtype was associated with CNS progression on univariate analysis (hazard ratio [HR] = 5.0, p = 0.008). On multivariate analysis, triple negative subtype (HR = 8.6, p = 0.001), Luminal B subtype (HR = 4.3, p = 0.03), and omission of whole-brain radiation therapy (HR = 3.7, p = 0.02) were associated with CNS progression. With respect to OS, Karnofsky Performance Status (KPS) ≤ 80% (HR = 2.0, p = 0.04) and progressive extracranial disease (HR = 3.1, p = 0.002) were significant on univariate analysis; KPS ≤ 80% (HR = 4.1, p = 0.0004), progressive extracranial disease (HR = 6.4, p < 0.0001), and triple negative subtype (HR = 2.9, p = 0.04) were significant on multivariate analysis. Although median survival times were consistent with those predicted by the breast cancer-specific Graded Prognostic Assessment (Breast-GPA) score, the addition of extracranial disease status further separated patient outcomes. Conclusions: Tumor subtype is associated with risk of CNS progression after SRS for breast cancer brain metastases. In addition to tumor subtype and KPS, which are incorporated into the Breast-GPA, progressive extracranial disease may be an important prognostic factor for OS.