Background: Pembrolizumab received FDA approval in 1L R/M HNSCC as monotherapy (P) in patients with combined positive score (CPS) ≥1, and in combination with platinum + 5-Fluorouracil (5-FU) chemotherapy (P + C) in the total population, based on KEYNOTE 048 (KN048) trial. Taking a US payer perspective, we evaluated the CE of P and P + C versus KN048 trial comparator cetuximab + platinum + 5-FU (EXTREME regimen), and other comparators commonly used in the US (i.e. cisplatin+docetaxel+cetuximab [TPEx regimen], platinum + paclitaxel/taxane [Pt + T] and platinum+5-FU [Pt + F]). Methods: A 3-state partitioned-survival model was used to project costs and outcomes over 20 years with a 3% annual discount rate. For P, P + C and EXTREME, health state occupancy was based on KN048 trial results with long-term parametric extrapolation of progression-free survival (PFS) and overall survival (OS) guided by statistical criteria. A network meta-analysis (NMA) was applied to the P and P + C interventions in KN048 to project the PFS and OS outcomes for other comparators. The time on treatment (ToT) for P, P+C and EXTREME was derived from the KN048 trial, whereas for other comparators, ToT was approximated by PFS. Costs of 1L and subsequent treatments, disease management, adverse event, and terminal care were included. Utilities were derived using the EuroQoL five-dimension data from KN048 and a US value set. Results: CE ratios, total and incremental costs and quality-adjusted life years (QALYs) from the base case analysis are summarized in the table below. P was more effective and less costly (i.e. dominant) versus EXTREME and TPEx. P + C was highly cost-effective versus EXTREME ($1,789/QALY) and TPEx regimen (dominant). CE ratios for both P and P + C versus all comparators were below a $100,000/QALY willingness-to-pay threshold. Probabilistic sensitivity analysis also showed a 100% CE probability for P and P + C at the $100,000/QALY threshold. Conclusions: P and P + C are cost-effective treatment options in the US with CE ratios below $100,000/QALY gained versus commonly used therapies in 1L R/M HNSCC.

^*CPS ≥1 R/M HNSCC ^**Total R/M HNSCC.