Survival outcomes for patients with extensive stage small cell lung cancer (ES-SCLC) treated with consolidative thoracic radiation therapy (cTRT) and chemoimmunotherapy (CIT): A population level study.

e20126 Background: CIT has been adopted as the first-line treatment for ES-SCLC, supported by clinical trials which showed significant survival benefits. A synergistic effect of cTRT + CIT is theorized to enhance survival outcomes, but real-world data supporting the routine use of cTRT + CIT is limited. This study aims to investigate the safety and effectiveness of patients with ES-SCLC treated with CIT + cTRT in routine clinical practice. Methods: We identified a cohort of ES-SCLC patients treated with CIT + cTRT, with treatment initiated from Sept 2019 to Nov 2023, using Glans-Look Research Database, a province wide lung cancer registry, from which baseline demographic, diagnostic, treatment, and outcome information were derived. The last day of follow up was Dec 10, 2024. Descriptive statistics and survival analyses were generated. Results: 50 patients were identified, median age at diagnosis was 68. At CIT initiation, 34 (68%) patients had ECOG ≤ 1 and 38 (76%) had baseline brain metastasis. 35 (70%) patients received durvalumab, 11 (22%) atezolizumab, and 4 (8%) alternate immune checkpoint inhibitors (ICI). All CIT used ICI with platinum-based chemotherapy and etoposide. The median time from CIT initiation to cTRT was 4.7 months. The total dose of cTRT varied, with most patients (n= 23) receiving 30Gy in 10 fractions. 4 patients received doses above 30Gy (40-60 Gy in 8-20 fractions) and 23 received doses below 30Gy (22.5-25 Gy in 5-10 fractions). The incidence of post-cTRT pneumonitis was n=9 (18%), induced by radiation (n=4), ICI (n=3) or mixed etiology (n=2); the majority were low grade (n=8; grade 1-2) and managed with outpatient steroids, but 1 incidence of grade 3 pneumonitis required hospitalization. 20 (40%) patients experienced clinically significant CIT-induced adverse events (AEs) requiring treatment modification/interruption. Serious AE (≥ grade 3) included myelosuppression (n=6), cardiac (n=1), gastrointestinal toxicity (n=5), sepsis (n=1), and paraparesis (n=1). The median overall survival (OS) and progression-free survival (PFS) post-CIT initiation were 21.3 and 11.7 months, respectively. The presence of baseline brain metastasis was associated with both worse OS (HR = 3.0, 95% CI 1.2-7.2, p = 0.015) and PFS (HR = 2.9, 95% CI 1.3-6.4, p = 0.008). The type of ICI, atezolizumab vs durvalumab, did not significantly impact OS (HR = 0.85, 95% CI 0.36-2, p = 0.7) or PFS (HR = 0.95, 95% CI 0.44-2.1, p = 0.9). Conclusions: Our study observed a high incidence of pneumonitis (18%) in this largest North American cohort of real-life ES-SCLC patients receiving CIT + cTRT. Pivotal trials of CIT did not permit cTRT and had reported pneumonitis rates of < 2 %. Most of our pneumonitis cases were low-grade and did not require hospitalization. Overall, CIT + cTRT appears to be well tolerated in this cohort of real world patients.