Clinical Outcomes of Patients with Metastatic Breast Cancer Treated with Hypo-Fractionated Liver Radiotherapy

IntroductionGrowing data support the safe and efficacious use of ablative radiotherapy in the setting of liver metastases, with some studies suggesting that patients with metastatic breast cancer (MBCa) do better than patients with metastases from other cancers. This study aims to retrospectively review clinical outcomes of patients with MBCa following liver radiotherapy (RT).Materials and MethodsPatients with MBCa who received liver hypo fractionated ablative RT between 2004 – 2020 were classified according to metastatic classification and treatment intent (i.e., oligo-metastatic (OM) or oligo-progressive (OP)). Demographics, disease characteristics and treatment characteristics were collated. Primary outcome was local control (LC) of treated metastases. Secondary outcomes included overall survival (OS), progression-free survival (PFS), and time to next line systemic therapy (ST), analyzed by univariate (UVA) and multi-variable analysis (MVA).ResultsThirty MBCa patients with 50 liver metastases treated with 5 – 10 fraction ablative intent RT were identified for analysis. Median follow-up was 14.6 months (range 0.9 - 156.2 months). Mean age was 55.6 years (range 32.1 - 79.3 years); 53% were ER+/HER2-ve and 33% HER2+ve. Class of metastatic disease was described as – induced (12 patients, 40%), repeat (15 patients, 50%) and de novo (3 patients, 10%) (1 synchronous, 2 metachronous). Indication of treatment was OP (73%) and OM (27%). Median size of treated liver metastases (LM) was 3.1 cm (range 1cm – 8.8 cm) and the median dose delivered was 40Gy (range 30Gy-60Gy). 1 and 3-year LC rates were 100%. Median OS was 57.7-months with size of treated liver metastases predictive of overall survival (HR 1.35, p=0.023) on UVA. Median time to progression post treatment was 4.8 months (0.8 – 114.7). Patients with induced OMD had a significantly higher rate of progression (HR 4.77, p=0.01) on UVA compared to others, which trended to significance on MVA (HR 3.23, p=0.051).ConclusionHypo-fractionated ablative liver RT in patients with MBCa provides safe, tolerable treatment with excellent LC. Further studies assessing the impact, ideal sequencing, and indications of RT in each metastatic class in MBCa are required.