Abstract Background: The real-world survival outcomes of first-line (1L) immunotherapy (IO)-based regimens for the treatment of advanced non-small cell lung cancer (aNSCLC) were assessed utilizing the Flatiron Health database from January 2011 to June 2023. Methods: Adult patients (pts) with aNSCLC receiving 1L IO monotherapy or single-agent IO + chemotherapy on or after January 1, 2016, were identified. Pts were excluded if they had EGFR/ALK mutations or unknown histological type. Overall survival (OS) and real-world progression-free survival (rwPFS) of 1L IO monotherapy and IO + chemotherapy were described using Kaplan-Meier analyses. Results: A total of 14,320 pts were included (5,166 pts receiving IO monotherapy; 9,154 pts receiving IO + chemotherapy). Among pts receiving IO monotherapy, the 1-, 2-, 3-, and 4-year OS rates were 52.3%, 36.5%, 27.4%, and 21.9%, respectively. The corresponding rwPFS rates were 29.2%, 17.5%, 12.7%, and 9.2%. Among pts receiving IO + chemotherapy, the 1-, 2-, 3-, and 4-year OS rates were 50.7%, 32.6%, 23.9%, and 19.2%. The corresponding rwPFS rates were 27.0%, 15.1%, 10.3%, and 7.8%. Table 1 presents the 4-year OS and rwPFS rates stratified by histological type, tumor programmed death ligand 1 (PD-L1) expression level, and Eastern Cooperative Oncology Group (ECOG) performance status. Patients with lower PD-L1 expression level (<1%), worse ECOG performance status (≥2), and squamous cell carcinoma had worse survival outcomes, regardless of the type of 1L treatment received. Conclusions: The real-world survival rates for patients with aNSCLC who were treated with 1L IO-based regimens were lower than those observed in pivotal trials, which indicates an unmet need for the management of newly-diagnosed aNSCLC. However, on average approximately 1 in 11 pts receiving IO monotherapy and 1 in 13 pts receiving IO + chemotherapy remained progression-free at the four year landmark and achieved an extended period of survival. Table: 4-year OS and rwPFS rates 1L IO monotherapy 1L IO + chemotherapy PD-L1 <1% PD-L1 ≥1-49% PD-L1 ≥50% PD-L1 <1% PD-L1 ≥1-49% PD-L1 ≥50% OS by histological type (sample size; 4-year rate, %) Squamous 122; 12.7 329; 14.0 814; 15.1 585; 11.7 647; 15.1 295; 23.3 Non-squamous 231; 16.7 516; 20.0 2563; 26.3 2263; 14.9 2058; 20.8 1313; 28.9 OS by ECOG performance status (sample size; 4-year rate, %) 0-1 193; 17.0 439; 20.8 1880; 27.6 1852; 16.8 1802; 21.9 1065; 28.0 ≥2 89; 6.7 261; 14.5 840; 12.7 478; 5.6 452; 11.1 241; 22.8 rwPFS by histological type (sample size; 4-year rate, %) Squamous 122; 7.6 329; 4.4 814; 6.8 585; 5.2 647; 8.3 295; 9.2 Non-squamous 231; 5.1 516; 10.0 2563; 11.2 2263; 4.3 2058; 6.3 1313; 14.7 rwPFS by ECOG performance status (sample size; 4-year rate, %) 0-1 193; 6.9 439; 10.4 1880; 11.9 1852; 5.4 1802; 6.8 1065; 14.5 ≥2 89; NA 261; 3.7 840; 5.0 478; 2.2 452; 3.9 241; 8.2 Citation Format: David Waterhouse, Saurabh Ray, Keith A. Betts, Sophie Gao, Yong Yuan, Manasvi Sundar, Shumin Rui, David Stenehjem. Real-world long-term survival outcomes of first-line immunotherapy-based regimens in advanced non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3819.