ESTRO 2025 - Abstract Book

S1450

Clinical - Lung

ESTRO 2025

treated in the real-world setting using the SEER database. We also investigated the effect of using radiotherapy on OS before and after this approval.

Material/Methods: ES-SCLC (TNM stage 4) patients treated after the FDA approval date for immunotherapy (timeframe: 2020-2021) and before (timeframe: 2015-2018) were identified from the SEER Research database, 17 Registries, Nov 2023 Sub. To investigate temporal prognostic trends and provide confidence in study findings, patients treated in timeframe before the FDA approval date for immunotherapy were divided into 2 cohorts; those treated in 2015–2016 and those treated in 2017–2018. The SEER database does not identify immunotherapy as a variable. However, we assumed that a significant proportion of patients treated after the FDA approval date for immunotherapy will have received immunotherapy in addition to chemotherapy. The primary endpoint was OS which was compared between groups using the Kaplan-Meier method and the Cox proportional hazards model. Results: Mean OS in patients treated after the FDA approval date for immunotherapy (n=1733) was 10.15 months (95% CI: 9.62–10.67) compared to 9.58 months (95% CI: 9.22–9.94) in patients treated in the 2-year timeframe immediately before the FDA approval date for immunotherapy (n= 2096); p<0.001 (Figure 1A). The survival difference (0.57 months) is smaller than in the IMpower133 trial (2 months) likely due to less fit patients and non-uniform use of immunotherapy. There were no significant differences in OS between patients treated in 2 timeframes before the FDA approval date for immunotherapy (2015–2016 and 2017–2018) providing moderate confidence that the survival difference reported above could be explained by immunotherapy use in routine care (Figure 1B). The addition of radiotherapy was associated with improvements in median OS for patients treated before (median OS: 14.39 vs 10.15; p<0.001) and after (median OS: 11.74 vs 9.58; p<0.001) the FDA approval date for immunotherapy; Figure 2A,2B.