Hypofractionated stereotactic radiation therapy showed high local control in breast cancer brain metastases.

PURPOSE: Although fractionated stereotactic radiation therapy (FSRT) remains understudied for the management of breast cancer brain metastases, this study aimed to investigate its therapeutic efficacy and safety in the context of contemporary systemic therapies. We enrolled patients with 1 to 10 brain lesions. METHODS AND MATERIALS: This was a prospective, single-arm, phase 2 trial involving 173 patients with breast cancer and 436 brain metastases, all treated with FSRT at a dose of 3 to 5 fractions of 8 Gy each. The primary endpoint was the local control rate, and secondary endpoints included the intracranial distant control rate, overall survival, and central nervous system progression-free survival. RESULTS: With a median follow-up of 15 months, the 1-year local control rate was 88.6% and the 1-year intracranial distant control rate was 52.1% (95% CI, 44.7%-60.8%). The median overall survival was 29 months (95% CI, 21-35 months), and the median central nervous system progression-free survival for patients with evaluable lesions was 12 months (95% CI, 9-16 months). Of the treated lesions, 27 out of 436 (6.2%) experienced radiation necrosis; no grade 3 or 4 FSRT-related adverse events were observed. Local control rates exceeded 86% at 1 year across all subtypes, whereas the intracranial distant metastasis-free survival was lower, ranging from 39.7% to 57.9%. CONCLUSIONS: In this single-institution trial, FSRT delivered in 3 to 5 fractions of 8 Gy each for breast cancer brain metastases yielded high local control with low rates of radiation necrosis in the background of modern systemic treatment.