Background: For advanced NSCLC patients (pts) with high (≥50%) PD-L1 expression, effective IO mono options with survival benefits are approved (pembrolizumab mono, current standard of care) and emerging (cemiplimab). In a recent Phase 3 trial, cemiplimab, a high-affinity, highly potent human PD-1 inhibitor approved for tx of advanced cutaneous squamous cell carcinoma, demonstrated significantly improved overall survival (OS) and progression-free survival (PFS) vs chemotherapy (CT) in advanced NSCLC pts with PD-L1 ≥50%. A systematic literature review and NMA were conducted to identify/compare the efficacy/safety from randomized controlled trials (RCTs) for cemiplimab vs pembrolizumab or other IO mono published 2010–19. Methods: Relevant RCTs were identified by searching Embase, MEDLINE, Cochrane, and conference proceedings with predefined search strategies according to ISPOR, NICE, and PRISMA guidelines. An NMA with time-varying hazard ratios (HRs) was performed for OS and PFS. Analyses were conducted for objective response rate (ORR), Grade (G) 3–5 all-cause adverse events (AE), G3–5 immune-mediated AE (IMAE) and discontinuation due to AEs (DAE). Fixed-effect models were used due to limited evidence. Results with standard constant HRs and various sensitivity analyses were conducted to account for differences in RCT designs and other txs. Results: The feasibility assessment determined that EMPOWER-Lung 1, KEYNOTE-024, and KEYNOTE-042 trials were eligible. IMpower110 was excluded since an incompatible PD-L1 assay (SP142) was used for pt selection. For 1L advanced NSCLC with PD-L1 ≥50%, cemiplimab was associated with significantly greater PFS and ORR, and comparable OS, G3–5 AEs, IMAEs, and all-cause DAEs vs pembrolizumab (Table). At 2 yrs, numerically more pts receiving cemiplimab vs pembrolizumab were alive (59% vs 49%) and significantly more were alive w/o progression (37% vs 18%). Conclusions: In advanced NSCLC pts with PD-L1 ≥50%, cemiplimab mono demonstrated significant improvements in PFS and ORR, and comparable OS, safety/tolerability vs pembrolizumab.