CLINICAL OUTCOMES OF BREAST BRAIN METASTASES BY SUBTYPE FOLLOWING LINAC BASED STEREOTACTIC RADIATION

Abstract BACKGROUND Management of breast cancer brain metastases has become an increasing concern due to improved systemic control. Failure patterns in the brain may vary by breast cancer subtype. OBJECTIVE In this study, we sought to distinguish our institutional clinical outcomes following stereotactic radiation by breast cancer subtype. METHODS A total of 180 breast cancer patients treated over 279 stereotactic sessions to 646 brain metastases were identified from our LINAC based stereotactic radiation institutional registry. Patients were treated between August 2004 and May 2019. Outcomes including distant brain metastases control (DC) as well as overall survival (OS) following stereotactic radiation were assessed from review of the clinical chart and radiologic examinations. RESULTS The median age of patients was 55 (range: 28-86 years). Subtypes in order of decreasing frequency were hormone receptor (HR)+ (n=64; 36%), HR+/HER2+ (n=47; 26%), triple negative (TN) (n=43; 24%), and HR-/HER2+ (n=26; 14%). TN patients had the shortest interval from systemic metastases to brain metastases diagnosis; HR-/HER2 + 16 months, HR+ 13.3 months, HR+/HER2 + 11 months, and TN 1.4 months (p=0.02). Median follow-up from brain metastases diagnosis was 21.2 months (range: 0.9-135.4 months). Twenty-four month Kaplan-Meier (KM) DC rates varied by subtype and were 49% (HR+/HER2+), 38% (HR+), 33% (HR-/HER2+) and 21% (TN) (p=0.0004), respectively. Similar differences were noted in OS with 24 month KM rates of 58% (HR+/HER2+), 51% (HR-/HER2+), 27% (HR+), and 14% (TN), p< 0.0001. A total of 26 patients (14%) were noted to undergo leptomeningeal disease (LMD) progression. No differences were noted by subtype and LMD progression (p=0.88). CONCLUSIONS In our institutional series of breast cancer brain metastases treated with stereotactic radiation, significant differences were noted in clinical outcomes by breast cancer subtype. HR+/HER2+ patients had the best DC and OS rates while outcomes were poorest for TN patients.