ESTRO 2025 - Abstract Book

S1534

Clinical – Mixed sites & palliation

ESTRO 2025

Turin, Italy. 9 Maastricht University Medical Center, Department of Radiation Oncology (Maastro Clinic), Research Institute for Oncology and Developmental Biology (GROW), Maastricht, Netherlands

Purpose/Objective: Stereotactic body radiotherapy (SBRT) is commonly combined with systemic therapy (STx) for managing oligometastatic cancer. However, the potential of SBRT to delay STx as a patient-centric outcome remains unclear. We conducted a systematic review and meta-analysis to evaluate the ability of SBRT to postpone STx. Material/Methods: This systematic review and meta-analysis followed PRISMA guidelines and was registered in PROSPERO (CRD42024580877). Studies published between January 2009 and January 2024 were included if they investigated metastasis- directed SBRT for oligometastatic cancer (≤5 metastases) without immediate STx in all patients or a defined subgroup. Eligible studies were prospective (any phase) or retrospective with ≥10 patients, reporting systemic therapy-free survival (STFS), progression-free survival, or overall survival. Literature searches were performed in PubMed and EMBASE. A weighted random-effects model was used to estimate pooled 1- and 2-year STFS rates. A meta-regression was performed to evaluate the impact of cancer subtype on STFS and quantify the proportion of heterogeneity explained by this variable. Results: From 3,351 records screened, 27 studies (2,018 patients) met inclusion criteria. These studies encompassed various cancer types and reported outcomes for SBRT without immediate STx (Table 1). Study designs included retrospective and prospective cohorts, single- and multi-institutional studies, and randomized and single-arm trials, with sample sizes ranging from 13 to 371 patients. Prostate cancer was the most frequently studied tumor type, followed by renal cell carcinoma and tumor-agnostic cohorts. A subset of 12 studies (962 patients, 628 events) provided 1- or 2-year STFS data for meta-analysis (Figure 1). The pooled 1- or 2-year STFS was 71.1% (95% CI: 58.3 – 82.6%) with high heterogeneity (I² = 93.5%, p < 0.0001). Subgroup analysis showed the highest STFS in renal cell carcinoma at 87.0% (95% CI: 76.2 – 95.2%, I² = 0%), followed by prostate cancer at 82.2% (moderate heterogeneity, I² = 52.5%). Other cancer types demonstrated lower pooled STFS (52.8%, I² = 97.5%). Meta-regression analysis indicated that cancer subtype accounted for 49% of heterogeneity, though significant residual heterogeneity remained (I² = 85.4%, p < 0.0001). While cancer subtype significantly contributed to the model (p = 0.011), no single subtype showed a significant difference from the reference category.