Stereotactic Body Radiotherapy Without Systemic Therapy for Oligometastatic Cancer: A Systematic Review and Meta-Analysis.

Importance: Metastasis-directed stereotactic body radiotherapy (SBRT) may be a viable strategy to defer systemic therapy in patients with oligometastatic cancer due to comorbidities, patient preferences, or concerns about adverse effects. To date, the evidence supporting this approach has not been comprehensively assessed. Objective: To evaluate systemic therapy-free survival (STFS) for different types of oligometastatic cancer after SBRT alone and to quantify adverse events, quality of life, and oncological outcomes. Data Sources: A systematic search of PubMed and EMBASE was conducted on July 10, 2024, to identify potentially eligible studies published after 2009. Forward and backward citation tracking was performed to identify additional relevant studies. Study Selection: Studies eligible for inclusion in the systematic review were retrospective or prospective with at least 10 patients who received metastasis-directed SBRT and no up-front systemic therapy for oligometastatic cancer (≤5 metastases) irrespective of primary tumor histology. Required outcomes being reported were STFS, progression-free survival, or overall survival. The subgroup of studies reporting STFS at 1 or 2 years were included in a meta-analysis of these pooled outcomes. Data Extraction and Synthesis: Two reviewers independently extracted data using predefined forms and followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A random-effects model was used for meta-analysis. Main Outcomes and Measures: The primary outcome of the meta-analysis was the pooled STFS rate at 1 or 2 years. Results: Of 29 unique studies (2074 unique patients) included in the systematic review, 13 (984 patients) contributed data to the meta-analysis. The pooled 1- or 2-year STFS rate was 69.7% (95% CI, 57.4%-80.9%) across cancer types. Renal cell cancer demonstrated the highest STFS rate (87.0%; 95% CI, 76.2%-95.2%), followed by prostate cancer (78.1%; 95% CI, 67.4%-87.3%), with lower rates in other cancer types. Among 20 studies reporting adverse events, rates of adverse effects of grade 3 or higher were absent in 15 of 19 studies (79%) and ranged from 2 of 103 (1.9%) to 3 of 34 patients (8.8%) among those that observed severe adverse events. Conclusions and Relevance: In this systematic review and meta-analysis, metastasis-directed SBRT alone was associated with meaningful STFS, particularly in patients with oligometastatic prostate or renal cell cancer, with low risks of treatment-related adverse events. These findings suggest that SBRT alone might be an acceptable option instead of immediate systemic therapy in selected patients with oligometastatic cancer.