NCTQ-02 PROGNOSIS IN BREAST CANCER BRAIN METASTASES: INFLUENCE OF MOLECULAR SUBTYPE, U-RPA CLASSIFICATION, AND RADIATION THERAPY

Abstract BACKGROUND The impact of breast cancer subtype, updated-recursive partitioning analysis (U-RPA) classification, and brain-directed radiation on the prognosis of patients with breast cancer brain metastases (BCBM) remains unclear. METHODS We retrospectively examined the overall survival (OS) after diagnosis and the first radiation therapy (RT), the hospital readmission-free survival (HRFS), and the intracranial progression-free survival (IPFS) in patients treated between 2017 and 2024. The association between breast cancer subtypes, U-RPA classes, the type of radiation received, and survival outcomes was assessed using multivariable Cox regression models. RESULTS Of 136 patients with BCBM, 71 received first-line RT. Patients with U-RPA class 3 had statistically significantly worse overall survival (OS) (HR, 4.38, p < 0.001) and RT OS (HR = 9.30, p = 0.002) compared to those with class 1. Triple-negative patients had worse BCBM OS compared to HR+/HER2- (HR = 0.45, p = 0.002), HR-/HER2+ (HR = 0.28, p = 0.002), and HR+/HER2+ (HR = 0.20, p < 0.001) patients. Triple-negative patients had worse RT OS compared to those with HR-/HER2+ (HR = 0.29, p = 0.018) and HR+/HER2+ (HR = 0.17, p = 0.002) tumors. There was no significant difference in BCBM OS (HR = 1.42, p = 0.319) or RT OS (HR = 0.99, p = 0.972) between stereotactic radiosurgery (SRS) and whole brain radiation therapy (WBRT). HRFS did not differ significantly between patients treated with SRS and WBRT (HR = 1.23, p = 0.738), although IPFS was worse in SRS-treated patients compared to those treated with WBRT (HR = 2.60, p = 0.043). CONCLUSION Molecular subtype and U-RPA classification are prognostic of outcomes. Triple-negative status and higher u-RPA class predict worse OS. HR+/HER2+ patients demonstrated the best OS of any group. There was no difference in OS according to RT modality.