Extended Follow-Up Analysis of First-Line Atezolizumab in Extensive-Stage Small Cell Lung Cancer: A Real-World Multicenter Prospective Cohort Study

Background: We previously reported the short-term real-world effectiveness and safety of first-line atezolizumab combined with chemotherapy in patients with extensive-stage small cell lung cancer (ES-SCLC). This study provides an updated analysis of the effectiveness, prognostic factors, and subsequent treatment patterns in first-line immunochemotherapy. Methods: This prospective multicenter observational study enrolled patients with ES-SCLC, diagnosed at seven university hospitals throughout Korea, between June 2021 and August 2022. Primary outcomes were 1-year overall survival (OS) and progression-free survival (PFS), whereas secondary outcomes included OS, objective response rate, disease control rate, second progression-free survival, and safety, evaluated based on established clinical guidelines. Results: A total of 100 ES-SCLC patients (median age, 69 years) were enrolled, with a median follow-up duration of 26.0 months. The median PFS and OS were 6.2 and 17.1 months, respectively, with a 1-year OS rate of 62.5%. Favorable prognostic factors for OS included partial response (PR) and stable disease (SD) as the best responses (SD: hazard ratio (HR), 0.79; PR: HR, 0.38) and a longer platinum-free interval (HR 0.84). Brain radiotherapy significantly improved OS in patients with brain metastases, whereas thoracic radiotherapy during first-line treatment tended to prolong survival in patients who responded to systemic treatment. Patients receiving second-line treatment after progression presented a significantly longer OS than did those receiving only best supportive care. Conclusion: This study outlined the real-world effectiveness and safety of first-line atezolizumab immunochemotherapy for ES-SCLC patients over an extended follow-up, noting that local treatment and post-progression therapy were associated with improved survival.