Prognostic Factors of Oligometastasis after Stereotactic Body Radiotherapy: Real-world Utility of the European Society for Radiotherapy and Oncology/European Organisation for Research and Treatment of Cancer Classification

Abstract Background The efficacy of local therapy for oligometastatic disease (OMD) remains unclear. This study aimed to evaluate the prognostic utility of the classification system for OMD and explore which groups may benefit from stereotactic body radiation therapy (SBRT). Methods The single-center retrospective study included 48 patients (55 sites) with solid tumors and 1–3 extracranial oligometastases, who underwent SBRT for all metastases at our institution between January 2018 and December 2021. OMD states were classified based on the European Society for Radiotherapy and Oncology and European Organisation for Research and Treatment of Cancer classification system. Local control (LC), overall survival (OS), and progression-free survival (PFS) for each group were analyzed using the Kaplan–Meier method. Acute and late adverse events (AEs) were evaluated. Results The median follow-up period was 14 months (range, 0–48 months). The number of patients in the de-novo, repeat, and induced OMD groups were 16, 19, and 13, respectively. The LC rates at 1-year for the entire, de-novo, repeat, and induced cohorts were 87.9%, 88.2%, 90.9%, and 83.9%, respectively. The 1-year PFS and OS for each group were 38.9%, 81.2%, and 61.0% and 87.1%, 29.9%, and 80.8%, respectively. Grade 2 or higher AEs occurred in five patients (10.4%). No grade 4 or 5 AEs were observed. Conclusions SBRT in patients with OMD was safe and highly effective for local control. Patients with repeat OMD demonstrated better PFS than other OMDs.