ESTRO 2025 - Abstract Book

S1440

Clinical - Lung

ESTRO 2025

4465

Digital Poster Impact of Immunotherapy in the Treatment of Oligometastatic NSCLC Treated with SBRT to all Metastatic Disease Sites Eva Ćirić, Jasna But-Hadzic Department of Radiation Oncology, Institute of Oncology Ljubljana, Ljubljana, Slovenia Purpose/Objective: The addition of local ablative therapy to standard systemic therapy in patients with oligometastatic non-small cell lung cancer (NSCLC) has been studied in several prospective trials and has been shown to improve survival in this patient population. However, few trials have been yet conducted in the era of immunotherapy. The aim of this single-center retrospective study was to analyse the impact of immunotherapy on survival of patients with de-novo oligometastatic NSCLC, as classified by ESTRO-EORTC oligometastatic disease classification, treated with stereotactic body radiotherapy (SBRT). Material/Methods: All patients with non-oncogene addicted synchronous and metachronous de novo oligometastatic NSCLC (OMD) treated at the Institute of Oncology Ljubljana with SBRT (with or without surgery in the case of brain metastasis) on all oligometastatic lesions and local ablative therapy on primary tumor (radiotherapy, chemoradiotherapy, or surgery) between January 2018 and December 2022 were included in the analysis. Data on clinical, tumor, and treatment characteristics were retrieved retrospectively using institutional medical records. The survival outcomes were calculated using Kaplan - Meier actuarial survival methods and Cox proportional-hazards models. Results: A total of 107 patients were identified, 53 with synchronous and 54 with metachronous oligometastases. Sixty-five patients (61%) had single and 42 (39%) had 2-5 oligometastases. The metastatic sites were brain in 51 (47%), bone in 23 (21%), lung in 19 (18%) and suprarenal glands in 8 (8%) patients. Squamous histology was found in 33% of patients, and non-squamous in 67%. PD-L1 expression was ≥50% in 23%, <50% in 72% and unknown in 5% of patients. Staging with PET/CT was done in 75% of patients. Of 46 (43%) patients who received any form of systemic therapy 29 had chemotherapy only and 17 had immunotherapy-based regimens. With a median follow-up of 17.6 months, the median progression-free survival (PFS) and overall survival (OS) for the entire cohort were 11.9 months (95% CI: 8.0-15.8) and 22.6 months (95% CI: 16.1-29.1), respectively. No tumor-related factor was associated with PFS, and only non-squamous histology was associated with improved OS (HR 0.58, p=0.036). Immunotherapy was the only treatment related factor significantly associated with improved PFS (HR 2.43, p=0.013) and OS (HR 2.7, p=0.032). Estimated median PFS for patients treated with and without immunotherapy was 21.7 and 9.8 (p=0.010) and median OS was not reached and 19.1 months (p=0.025).