ESTRO 2025 - Abstract Book

S1452

Clinical - Lung

ESTRO 2025

of radiotherapy to primary thoracic disease and/or metastatic tumors in paitents with metastatic small cell lung cancer (SCLC). 2 Material/Methods: We retrospectively reviewed the medical records, biopsy or surgical tumor samples of each patient with SCLC treated at Taipei Medical University Hospital, Taiwan between January 2014 and December 2023. Inclusion criteria were extensive stage SCLC and limited stage SCLC patients who eventually develop distant metastases and receive radiotherapy to primary thoracic disease (30~66 Gray / 10~33 fractions) and/or metastases (20~50 Gray / 4~25 fractions) with consecutive clinical and imaging follow-up within 4 months. Disease-free interval (DFI) between frontline treatment and recurrence was determined for each patient. Overall survival (OS) and progression-free survival (PFS) were calculated using the Kaplan–Meier analysis, and a log-rank test was used for group comparisons. Cox proportional hazard regression was performed to examine the effects of variables. Results: Thirteen patients were enrolled. Table 1 shows the clinical characteristic of our preliminary study, including median age of 65, 84.6% of patients were male, smokers, and extensive stage. Eight patients found relapsed SCLC within a year. Proportion of cohort receiving immunotherapy, radiotherapy to primary thoracic disease and metastases were 46.2%, 46.2%, and 69.2% respectively. Kaplan–Meier analyses showed both radiotherapy to primary thoracic disease (log-rank p = 0.013) and metastases (log-rank p = 0.000) may associated with superior 2-year OS. No significant factors associated with PFS. In multivariate analyses, radiotherapy to primary thoracic disease (hazard ratio [HR] = 0.147; p = 0.025) was the only factor independently associated with superior 2-year OS (Figure 1), while radiotherapy to metastases (HR = 0.000; p = 0.883) was insignificant.