Outcomes of extra-cranial stereotactic body radiotherapy for metastatic breast cancer: Treatment indication matters

Background and purpose: To summarize the clinical outcomes of stereotactic body radiotherapy (SBRT) for metastatic breast cancer (mBC) from a large institution. Materials and methods: Patients with mBC who received extra-cranial SBRT to metastatic lesions from 2011 to 2017 were identified. Treatment indications were: oligometastases, oligoprogression, and local control of dominant tumor (CDT). Endpoints included overall survival (OS), progression-free survival (PFS), local control (LC) and cumulative incidence of starting/changing chemo or hormonal therapy (SCT). Univariate and multivariate analyses were used to identify predictive factors. Results: We analyzed 120 patients (193 treated metastatic lesions) with a median follow up of 15.25 months. 1-and 2-year LC rates were 89% and 86.6%, respectively. 1-and 2-year OS rates were 83.5% and 70%, respectively, with treatment indication and molecular subtype being the predictive fac-tors on MVA. 1-year OS was 91.0%, 78.5% and 63.9% for oligometastases, oligoprogression and CDT, respectively (p = 0.003). The worst OS was seen in basal subtype with 1-and 2-year OS rates of 59.2% and 39.5% (p = 0.01). Treatment indication was found to be predictive for PFS and lower rates of SCT on MVA. 1-and 2-year PFS rates were 45% and 32%, respectively. The 1-year PFS for oligometastases, oligoprogression, and CDT was 66%, 19.6%, and 14.3%, respectively (p < 0.001). The cumulative incidence of SCT at 1-year was 12% for oligometastases, 39.7% for oligoprogression and 53.3% for CDT (p < 0.001). Conclusion: Patients treated for oligometastases have better OS and PFS than those treated for oligopro-gression or CDT. SBRT may delay SCT in mBC patients, particularly those with oligometastases. SBRT pro-vided an excellent LC in mBC patients. Crown Copyright (c) 2021 Published by Elsevier B.V. All rights reserved. Radiotherapy and Oncology 161 (2021) 159-165

Automated summary

SBRT treatment for metastatic breast cancer patients showed good overall survival and progression-free survival rates. SBRT can delay the start of systemic therapy for these patients.