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Background Despite poor prognosis, there were no advances in treatment options that improved outcomes for patients with ES-SCLC beyond chemotherapy 1 until the approval of immune checkpoint inhibitors (ICIs) as first-line treatment for ES-SCLC in 2019 and the approval of tarlatamab (a DLL3-targeting T-cell engager) in the second-line setting or beyond in 2024.2–4 There is a lack of real-world data describing the contemporary treatment landscape in ES-SCLC. We report real-world treatment patterns of systemic therapies for ES-SCLC in the United States from 2018 to 2023, with a focus on utilization of ICIs.Methods This retrospective, observational cohort study used structured oncology electronic medical record data to identify patients with ES-SCLC who initiated first-line systemic anticancer therapy (the index event) between October 1, 2018, and June 30, 2023, in the United States. A validated tumor-agnostic algorithm adapted for SCLC was used to derive treatment regimens and lines of therapy based on the order of systemic anticancer therapies received. The utilization of ICIs was defined as any systemic treatment regimen containing an anti-PD-(L)1 or anti-CTLA-4 antibody. Descriptive statistics were used for patient demographics, baseline clinical characteristics, and treatment distribution. Time to next treatment (TTNT) was assessed for select treatment regimens using the Kaplan-Meier method.Results Of 1969 patients included, mean age at ES-SCLC diagnosis was 67.5 years and median follow-up from index to last recorded visit during the study period was 7 months. Treatment patterns are shown in the Table ( table 1). As first-line treatment, 1407 patients (71.5%) received an ICI-containing regimen and 560 patients (28.4%) received chemotherapy without an ICI. Of those who advanced to second- and third-line treatments, 280 of 620 patients (45.2%) and 49 of 186 patients (26.3%), respectively, received an ICI-containing treatment regimen. Median TTNT (95% CI) with first-line atezolizumab+carboplatin+etoposide (n=1229) and durvalumab plus platinum-based chemotherapy (n=101) were 183 (176–191) days and 190 (163–211) days, respectively. Among patients receiving second-line therapy, median TTNT (95% CI) for atezolizumab+carboplatin+etoposide was 161 (92–201) days for patients with a chemotherapy-free interval (CTFI) >6 months (n=23) and 129 (123–181) days for those with CTFI ≤6 months (n=85).Conclusions This study showed that while more than 70% of patients with ES-SCLC received ICI-containing regimens as first-line treatment, prognosis remains poor, especially for those who progress on first-line treatment within 6 months. Novel therapeutic agents, such as DLL3-targeting T-cell engagers, may help to alleviate the high unmet need in this patient population.Acknowledgements Medical writing assistance was provided by Aisling Towell, PhD, of ICON plc (Blue Bell, PA, USA). This assistance was funded by Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA.References Arriola E, Trigo JM, Sanchez-Gastaldo A, et al. Prognostic value of clinical staging according to TNM in patients with SCLC: a real-world surveillance epidemiology and end-results database analysis. JTO Clin Res Rep. 2022;3:100266.He J, Hu Q. Progress in the clinical application of immune checkpoint inhibitors in small cell lung cancer. Front Immunol. 2023;14:1126582.Mathieu L, Shah S, Pai-Scherf L, et al. FDA approval summary: atezolizumab and durvalumab in combination with platinum-based chemotherapy in extensive stage small cell lung cancer. Oncologist 2021;26:433-8.Imdelltra (tarlatamab). Full Prescribing Information, Amgen Inc, Thousand Oaks, CA, USA, 2024.Abstract 415 Table 1