Factors associated with local failure after stereotactic radiation to the surgical bed of patients with a single breast cancer metastasis

Introduction: Breast cancer brain metastases (BCBM) are increasingly common due to improved systemic therapies prolonging survival. This study evaluates local control and factors influencing outcomes in patients with resected BCBM treated with postoperative stereotactic radiotherapy (SRT). Methods: A retrospective review included 62 patients with single resected BCBM treated with postoperative SRT from 2010 to 2022. The median follow-up was 28 months (range, 14-43). Variables analyzed included tumor size, biology, surgical corridor inclusion, radiation dose, and timing of SRT. Multivariable analysis was conducted using Cox regression. Results: Local control at 12 months was 70.9%, with a median progression-free time of 13 months (95% CI: 9-21). Intracranial failure occurred in 41.6%. HER2-positive tumors were associated with better local control (HR: 0.76, p = 0.032), as were BED > 40 Gy (HR: 0.65, p = 0.028) and shorter intervals between surgery and SRT (<28 days, HR: 2.7 for delays >28 days, p = 0.015). Larger tumors (>5 cm, HR: 2.1, p = 0.021) and cystic lesions (HR: 1.5, p = 0.13) were associated with poorer outcomes. Surgical corridor inclusion improved control but was not significant on multivariable analysis. Radiation necrosis occurred in 13% of patients, predominantly asymptomatic. Conclusion: Postoperative SRT offers reasonable control of BCBM. Factors such as HER2 positivity, timely SRT, and higher BED doses significantly affect outcomes. Future research should optimize dosimetric strategies and integrate systemic therapy to enhance local and intracranial control.