ESTRO 2025 - Abstract Book

S1574

Clinical – Mixed sites & palliation

ESTRO 2025

Our aim was to evaluate the tolerability and the efficacy of radiotherapy in a cohort of oligometastatic thymic tumors.

Material/Methods: We retrospectively reviewed the records of consecutive oligometastatic patients who underwent external radiotherapy (either SBRT or normo/hypo-fractionated external RT) for a thymic tumor between January 2005 and June 2024 at our 2 Institutions (Gustave Roussy Cancer Campus, Paris, France and AOU-Careggi, Florence, Italy). Oligometastatic disease was defined as per ESTRO/EORTC classification [1]. Patients’ and treatment -related characteristics were collected. Adverse events (AEs) were graded according to CTCAE v.5. Survival outcomes were calculated from end of RT and estimated by Kaplan-Meier analysis. Results: Forty-six patients were included (median age, 52 years, [range: 17-77]), comprising 115 treated lesions. Patients and treatment characteristics are summarized in Table 1. Pathologic diagnosis was thymoma in 35 patients (76%), thymic carcinoma in 7 patients (15%) and thymic neuroendocrine tumor in 4 patients (9%). Most common treated metastatic sites were intrathoracic pleura (77% of lesions) and bone (10% of lesions). RT was administered mostly for oligorecurrent disease (72% of treatments) by SBRT (87% of lesions). Median RT prescription dose was 30 Gy (range: 18-60Gy) in 5 fractions (range: 1-30). Median BED was 48 Gy (range: 23.4-115.5 Gy). After a median follow-up of 36 months (range: 2-243), 8 (7%) local failures occurred, whereas the most frequent failure after RT was pleural (53%). 1-years and 3-years Progression Free Survival (PFS) were 53% and 25%; 1-years and 3-years Overall Survival (OS) were 95% and 84%. 1-year and 3-years local control (LC) rates were 94% and 93%. 1-year and 3-years distant control rates were 82% and 69%, respectively. Median time to subsequent systemic therapy was 11 months (range: 2-82). No RT-related severe AEs were observed. Univariate analysis showed that non-thymoma histology was a predictor of LC and PFS (p=0.011 and 0.024, respectively) and that oligoprogressive disease and the number of previous chemotherapy lines for metastatic disease were predictors of PFS (p=0.022 and 0.012, respectively). No predictive factors were found at multivariate analysis.