Predictors of treatment response and overall survival in patients with breast cancer brain metastases treated with stereotactic radiosurgery: a prospective study using the NeuroPoint Alliance SRS Registry

OBJECTIVE The aim of this study was to evaluate mortality and progression outcomes in patients undergoing stereotactic radiosurgery (SRS) for breast cancer brain metastases and to identify associated risk factors using a national quality registry. METHODS The NeuroPoint Alliance (NPA) SRS Registry was employed for this study, which conducted prospective enrollment of patients undergoing SRS at 16 participating centers from 2017 to 2024. Outcomes of interest included the post-SRS EQ-5D score change, overall survival, local progression, out-of-field progression, and overall intracranial progression. For all time-to-event analyses, Kaplan-Meier curves and multivariable Cox regressions with hazard ratios were used. RESULTS A total of 138 patients (127 female, mean age 59.8 years) were identified; 46.4% had a single lesion, 42.0% had 2–4 lesions, and 11.6% had ≥ 5 lesions, while 87.0% had a Karnofsky Performance Status (KPS) score between 80 and 100. The median overall survival was 17.9 months, and independent predictors of all-cause mortality included a KPS score ≤ 90 (HR 6.73) and diabetes mellitus (HR 3.35). The median time to local progression was 19.8 months. More than 5 lesions at baseline (HR 9.03) and a marginal dose ≤ 17.6 Gy (HR 8.00) were predictive of local recurrence. The median was not reached for out-of-field progression, and predictors included ≥ 2 lesions at the time of SRS (HR 3.20) and a marginal dose ≤ 17.6 Gy (HR 4.61). At the final follow-up assessment, 17.1% of patients experienced no change according to the EQ-5D, while 34.3% had improvement, 11.4% had mixed results, and 37.1% had worsened health. In the multivariable linear regression model, pre-SRS resection (r = 1.92) and baseline EQ-5D score (r = 1.29) were statistically significant predictors of quality of life at the final follow-up assessment. CONCLUSIONS Using real-world data from the NPA SRS Registry, this study demonstrated comparable outcomes in patients who underwent SRS for breast cancer brain metastases compared with those of previous literature. The number of lesions at the time of SRS and the marginal dose were independent risk factors for local recurrence, out-of-field progression, and overall intracranial progression. Pre-SRS resection and baseline EQ-5D score were independent predictors of quality of life following SRS.