Real-world second-line treatment patterns and outcomes by platinum sensitivity in extensive-stage small cell lung cancer in the post-immunotherapy era.

8083 Background: Platinum-based chemotherapy (PBC) with checkpoint inhibitor (CPI) is standard first-line (1L) treatment for extensive-stage small cell lung cancer (ES-SCLC), though relapse is common. Second-line (2L) treatment selection is determined by platinum sensitivity status, with guidelines based on pre-CPI data, and the benefit of any CPI continuation is unknown. This study examined treatment patterns and real-world (rw) outcomes for patients following 1L PBC +/- CPI among platinum-sensitive (PS) patients, including the impact of continuing a CPI with platinum rechallenge. Methods: This retrospective study used EHR-derived US Flatiron Health Research Database. Eligible patients were diagnosed with ES-SCLC between January 1, 2018, and September 9, 2025, received 2L treatment following 1L PBC with a calculable platinum sensitivity and had a minimum potential follow up of 120 days. Platinum sensitivity was defined by a chemotherapy-free interval of ≥ 180 days, based on the last order or administration of 1L PBC to first real-world progression event prior to 2L initiation. Real-world response rate (rwRR), progression free survival (rwPFS) and overall survival (rwOS) were described based on 2L regimen class for patients with PS disease, and were compared via HR for platinum rechallenge with CPI continuation versus without. Time-to-event outcomes were analyzed using Kaplan-Meier methods, with medians and 95% CI reported for the overall cohort and subgroups of interest. Results: Among 5,126 eligible patients, 884 (17%) had PS and 4,242 (83%) had platinum refractory (PR) disease. Most patients (73%) received CPI with PBC in 1L. Patients with PR had worse outcomes than PS (rwPFS, 2.7 95% CI, 2.6-2.8 vs 5.5 95% CI, 5.3-5.7 mo; rwOS, 4.7 95% CI, 4.5-4.9 vs 11.2 95% CI, 10.6-12.4 mo). Among PS patients with 1L CPI exposure (n=666), 48% received 2L PBC, and 41% of 2L PBC continued a CPI. Clinical characteristics in PS disease were similar across classes of 2L regimen. Of patients with PS disease who had 1L CPI exposure, 81% had at least 1 response assessment during the study period. Of PBC patients, rwRR was 52% among CPI treated and 58% without CPI. 2L rwPFS and rwOS were similar regardless of CPI continuation (Table). Conclusions: In this large real-world study, nearly half of patients with PS disease were rechallenged with PBC in 2L, and CPI continuation was common despite limited evidence. CPI continuation did not improve response, progression, or survival, suggesting no additional benefit and highlighting the need for prospective data to guide post-CPI treatment in PS ES-SCLC. Outcome 2L rwPFS median, mo (95% CI) Unadjusted HR (95% CI) P value 2L rwOS median, mo (95% CI) Unadjusted HR (95% CI) P value PBC with CPI (n=112) 5.6 (5.4-6.2) - - 12.3 (11.0-15.9) - - PBC without CPI (n=149) 6.0 (5.6-6.6) 0.97(0.76, 1.25) 0.80 12.9 (11.0-15.3) 1.04 (0.80, 1.35) 0.80