Background: The PD-1 inhibitor pembrolizumab is currently approved as first-line monotherapy for patients with R/M HNSCC whose tumors express PD-L1 combined positive score (CPS) ≥1. In a phase 1b/2 trial (NCT02501096) of pembrolizumab plus lenvatinib (multikinase inhibitor of VEGFR 1-3, FGFR 1-4, PDGFRa, RET, and KIT) in solid tumors, the combination demonstrated promising antitumor activity and a manageable safety profile in patients with HNSCC. LEAP-010 (NCT04199104) is a randomized, double-blind, placebo-controlled, phase 3 study that will evaluate the efficacy and safety of first-line pembrolizumab with or without lenvatinib in patients with PD-L1–positive R/M HNSCC. Methods: Key eligibility criteria include histologically confirmed R/M HNSCC incurable by local therapies, PD-L1–positive tumor (CPS ≥1) as determined by central laboratory, measurable disease as assessed by blinded independent central review (BICR) per RECIST v1.1, and ECOG performance status (PS) 0 or 1. Patients will be randomly assigned 1:1 to pembrolizumab plus lenvatinib or pembrolizumab plus placebo. Randomization will be stratified by PD-L1 status defined by tumor proportion score ( < 50% vs ≥50%), human papillomavirus status for oropharynx cancer (positive vs negative), and ECOG PS (0 or 1). Patients will receive intravenous pembrolizumab 200 mg every 3 weeks for 35 cycles (~2 years) and oral lenvatinib 20 mg or placebo once daily; patients may continue to receive lenvatinib or placebo after pembrolizumab treatment is complete. Treatment will continue until BICR-verified disease progression or unacceptable toxicity. Pembrolizumab retreatment (second course) for 17 additional cycles will be allowed for eligible patients who stop pembrolizumab and subsequently experience BICR-verified disease progression. These patients could have stopped treatment with stable disease, partial response, or complete response or after 35 cycles of pembrolizumab for reasons other than disease progression or toxicity. Tumor imaging assessment will be performed at week 6, then every 6 weeks until 1 year, and thereafter every 9 weeks. Primary end points are objective response rate and progression-free survival, assessed by BICR per RECIST v1.1, and overall survival. Secondary end points are duration of response and safety and tolerability. Recruitment is ongoing; planned enrollment is ~500 patients. Clinical trial information: NCT04199104.