Simple SummaryLocal ablative liver radiotherapy is increasingly being used in the setting of metastatic disease, primarily to prevent local disease progression and potentially to improve patient survival. There is a paucity of data specifically reporting the role of liver-directed ablative radiotherapy in metastatic breast cancer. The aim of this retrospective review was to report a single institutional experience in the use of hypo-fractionated liver radiotherapy, patient and treatment descriptors and treatment and disease outcomes. The study describes an excellent 1-year local control rate (100%), with an acceptable acute side-effect profile. Size of liver metastases was predictive of survival, with class of metastatic disease predictive for disease progression. Further prospective studies are required to assess the impact of metastatic classification on the indication of local ablative therapies, sequencing and outcomes post treatment in patients with metastatic breast cancer.AbstractPurpose: To retrospectively review the clinical outcomes of patients with metastatic breast cancer (MBCa) following liver directed ablative intent radiotherapy (RT). Methods: Demographics, disease and treatment characteristics of patients with MBCa who received liver metastasis (LM) directed ablative RT between 2004–2020 were analysed. The primary outcome was local control (LC), secondary outcomes included overall survival (OS) and progression-free survival (PFS) analyzed by univariate (UVA) and multi-variable analysis (MVA). Results: Thirty MBCa patients with 50 LM treated with 5–10 fraction RT were identified. Median follow-up was 14.6 (range 0.9–156.2) months. Class of metastatic disease was described as induced (12 patients, 40%), repeat (15 patients, 50%) and de novo (three patients, 10%). Median size of treated LM was 3.1 cm (range 1–8.8 cm) and median biologically effective dose delivered was 122 (Q1–Q3; 98–174) Gy3. One-year LC rate was 100%. One year and two-year survival was 89% and 63%, respectively, with size of treated LM predictive of OS (HR 1.35,p= 0.023) on UVA. Patients with induced OMD had a significantly higher rate of progression (HR 4.77,p= 0.01) on UVA, trending to significance on MVA (HR 3.23,p= 0.051). Conclusions: Hypo-fractionated ablative liver RT in patients with MBCa provides safe, tolerable treatment with excellent LC.