Abstract PS14-02: A Prospective Phase II Trial of Hypofractionated Stereotactic Radiotherapy (FSRT) for Patients with 1-10 Brain Metastases from Breast Cancer

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Abstract Purpose: Single-fraction stereotactic radiotherapy (SRT) is widely recommended in modern breast cancer brain metastasis treatment for 1-4 lesions, while hypofractionated SRT (FSRT) is rarely reported. This study aims to evaluate the efficacy and safety of FSRT in patients with 1-10 brain metastases from breast cancer. Methods and Materials: From March 2019 to August 2023, we conducted a prospective, single-arm, phase II trial of FSRT in BM patients from breast cancer. Patients received FSRT delivered at 8 Gy per fraction in 3-5 fractions. The main inclusion criteria were breast cancer patients with 1-10 brain metastases. The primary endpoint was the local control (LC) rate, and the secondary endpoints included intracranial distant control, intracranial progression-free survival (iPFS), overall survival (OS), treatment-related toxicities, and assessments of neurocognitive function. The study is registered at clinicaltrials.gov with the identifier NCT04061408. Results: A total of 173 patients with 436 brain lesions underwent treatment with FSRT. The median age of patients was 51 years (IQR 43-59), of which 16.1% (28/173) had 5-10 lesions, and 30.0% (52/173) had the largest lesion over 2 cm. As of February 2024, at a median follow-up time of 15 months (IQR: 8-29 months), the local control rate at 1 year and 2 years was 88.6% (95% CI: 83.6-93.9%) and 77.1% (95% CI: 69.4-85.6%), respectively. The intracranial distant control at 1 year and 2 years was 51.8% (95% CI: 44.5-60.5%) and 26.7% (95% CI: 19.5-36.6%), respectively. The median OS for these patients was 29 months (95% CI: 21-36 months); the estimate of OS at 1 year and 2 years was 73.8% (95% CI: 67.2-80.9%) and 55.3% (95% CI: 46.4-65.8%), respectively. We included age, KPS score, presence of neurological symptoms, presence of extracranial metastases, molecular subtypes, number of lesions, maximum tumor diameter and total volume of lesions into multivariate regression analysis, and found that KPS was the only prognostic factor associated with local control rate. Among the 137 patients with evaluable lesions, the optimal treatment response was assessed by RANO-BM criteria. Except for 10 patients who did not have efficacy evaluation data, 33 patients (24.1%) achieved CR, 72 patients (52.6%) achieved PR, 18 patients (13.1%) achieved SD, and 4 patients (3.1%) were evaluated as PD. The median iPFS time for these patients with evaluable lesions was 11 months (95% CI: 9-15 months). Among the treated lesions, 27 cases out of 436 lesions (6.2%) experienced radiation necrosis. No grade 3 or 4 adverse events related to FSRT occurred in this study. Conclusions: This study demonstrated that FSRT treatment for breast cancer brain metastasis with 1-10 lesions is safe and effective option with excellent local control and a lower risk of radation necrosis. Citation Format: Jin Meng, Zhaozhi Yang, Li Zhang, Wei Shi, Jingyao Chen, Xiaofang Wang, Xingxing Chen, Xin Mei, Jinli Ma, Zhen Zhang, Zhimin Shao, Xiaomao Guo, Xiaoli Yu, Zhaozhi Yang. A Prospective Phase II Trial of Hypofractionated Stereotactic Radiotherapy (FSRT) for Patients with 1-10 Brain Metastases from Breast Cancer [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr PS14-02.

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