RADT-17. PATTERNS OF CARE AND SURVIVAL OUTCOME IN PATIENTS WITH BRAIN METASTASES FROM BREAST CANCER (KROG1612 STUDY)

Abstract BACKGROUND Brain metastases (BM) from breast cancer (BC) present a clinical challenge due to diverse prognosis, largely influenced by molecular subtype. We aimed to analyze evolving treatment patterns, survival outcomes, and prognostic factors in BC patients with BM. METHODS This multicenter study reviewed 730 patients diagnosed with BM between 2000 and 2014 across 17 Korean institutions. Initial and salvage brain-directed treatments, including whole-brain radiotherapy (WBRT), stereotactic radiosurgery (SRS), fractionated stereotactic radiotherapy (FSRT), and systemic therapy, were analyzed. Overall survival (OS) was estimated from BM diagnosis. Median follow-up duration was 11.9 months. Cox regression and recursive partitioning analysis identified key prognostic factors. RESULTS Median OS was 15.0 months. Over time, WBRT usage declined (80.0% in 2005 to 41.1% in 2014), while SRS/FSRT increased (13.3% to 34.7%). Poor prognostic indicators included histologic grade 3, extracranial metastasis, >4 BMs, hormone receptor (HR) negativity, HER2 negativity, and short interval (<30 months) between primary BC and BM diagnosis. In patients with late BM (≥30 months from primary diagnosis), WBRT was associated with improved OS. Triple-negative BC had the highest 1-year distant intracranial failure rate (69.6%). Initial WBRT reduced development of new BM, particularly in HR+/HER2– patients. Anti-HER2 therapy significantly reduced new BM risk. For patients with 1–10 BMs, number of lesion(s) and use of WBRT were not independent predictors of OS. However, salvage brain-directed treatment, mainly SRS/FSRT, extended OS by a median of 14.3 months. Furthermore, systemic therapy after salvage WBRT conferred additional survival benefit. A novel prognostic model incorporating extracranial control, primary tumor status, and salvage WBRT dose stratified patients with recurrent BM into distinct survival groups. CONCLUSIONS Molecular subtype and extracranial disease burden are key drivers of survival in BC-BM. Treatment patterns have shifted toward individualized strategies, with salvage SRS/FSRT and systemic therapy contributing meaningfully to survival improvement.