Salvage stereotactic radiosurgery (SRS) after previous whole-brain radiation therapy (WBRT) for breast cancer brain metastases: Outcomes and prognostic factors including tumor phenotype.

Abstract

581 Background: Salvage SRS is often considered in breast cancer patients (pts) previously treated with WBRT for brain metastases. The goal of this study was to analyze clinical outcomes and prognostic factors for survival in the salvage setting. Methods: We retrospectively examined all breast cancer pts who underwent SRS at DF/BWCC between 2000 and 2010. We identified 79 consecutive female pts who received salvage SRS (interval of > 3 months after initial therapy), 76 of whom (96%) received prior WBRT. Overall survival (OS) and CNS progression-free survival was calculated from the date of SRS using the Kaplan-Meier method. Prognostic factors were evaluated using the Cox proportional hazards model. Results: Median age was 50.5 years. Subtype distribution was: ER+, 46; HER2+, 27; triple negative, 8). 97% had a KPS ≥70%. 95% had extracranial metastases at the time of SRS, 81% at other visceral sites (lung/pleura/liver). 48% had stable extracranial disease at the time of SRS. Median interval from WBRT to SRS was 8.4 months. Median follow-up for survivors was 16.7 months. Median CNS progression-free survival was 5.7 months (IQR 3.6-11 months) and median OS was 9.8 months (IQR 3.8-18 months). 82% of evaluable pts received further systemic therapy after SRS. 92% of patients were in RPA class II. RPA class was not found to be a useful prognostic index in this population. Median OS in RPA class II pts was 10.4 months. HER2 status (adjusted HR 2.4, p=0.008) and extracranial disease status (adjusted HR 2.7, p=0.004) were significant prognostic factors for survival on multivariate analysis. Conclusions: In patients with good KPS, salvage SRS at the time of CNS recurrence should be strongly considered. HER2 positivity and status of extracranial disease are prognostic factors for survival following SRS in the salvage setting after prior WBRT. Prognostic factors for OS. Univariate Multivariate HR P value HR P value Age >65 y 3.4 0.02 1.8 0.3 Extracranial disease Progessing 2.9 <0.001 2.7 0.004 Stable 1 HER2+ Yes 1 No 2.3 0.002 2.4 0.008 ER+ Yes 0.73 0.2 No 1 Triple-negative Yes 3.8 0.001 1.6 0.3 No 1 KPS <80% 4.2 <0.001 1.9 0.11 N lesions treated SRS 1.1 0.76 Time to SRS 1.0 0.77