Effect of tumor subtype on overall survival in brain metastatic breast cancer patients treated with cranial irradiation.

Abstract

74 Background: Brain metastatic breast cancer (BMBC) is often treated with whole brain radiation therapy (WBRT), stereotactic radiosurgery (SRS) or both. Breast cancer tumor subtypes defined by hormone receptor (HR) and HER2 status have an important prognostic role in metastatic disease. It is unclear if tumor subtypes have a prognostic role in patients receiving WBRT or SRS. We aimed to investigate the association between breast cancer subtype and overall survival (OS) among BMBC patients treated with WBRT and SRS. Methods: In a single-institution cohort study, BMBC patients treated with WBRT/SRS during 1997-2013 were identified. Clinico-pathological characteristics and survival information were prospectively collected. Tumor subtype category were defined as HR+/HER2-, HER2+/HR+, HER2+/HR- and triple negative (TN). WBRT category patients received that modality and SRS category patients, only SRS for treatment of brain metastases. OS is defined as time from diagnosis of brain metastasis to death or last follow-up. We conducted univariate analyses using the Kaplan-Meier method and log-rank tests and multivariate analysis using Cox proportional hazards models. Results: Among 193 BMBC patients who received WBRT or SRS, 62 received just SRS, and among them, 45% was HR+/HER2-. The distribution of subtypes was similar in WBRT patients. The median OS in SRS group was 15 months (95% CI 11-18) compared to WBRT with 10 months (95% CI 7-14) (p=0.03). Among patients receiving WBRT, median OS in HER2+/HR- tumor was 30 months (95% CI 13-37), HER2+/HR+ tumor - 14 months (95% CI 5-24), HER2-/HR+ tumor - 8 months (95% CI 4-11) and TN - 5 months (95% CI 3-9) (P=0.0003). There was no significant difference in OS between the breast cancer subtypes among SRS patients: median OS among patients with HER2+/HR- tumor was 11 months (95% CI 5–27), HER2+/HR+ tumor - 25 months (95% CI 7-32), HER2-/HR+ tumor - 18 months (95% CI 14-32), and TN - 12 months (95% CI 3-24) (p=0.07). Conclusions: Among patients with BMBC,tumor subtype is a prognostic factor for survival in those who received WBRT. Tumor subtype provided no prognostic information for those who were treated with only SRS.