Ficerafusp alfa is directed against two targets, Epidermal Growth Factor Receptor (EGFR) and Transforming Growth Factor beta (TGF-β). This study intends to evaluate the safety and efficacy of ficerafusp alfa in combination with pembrolizumab versus placebo with pembrolizumab in 1L PD-L1-positive, recurrent or metastatic Head and Neck Squamous Cell Carcinoma (HNSCC).

The mechanism of action of ficerafusp alfa involves dual targeting of two cancer targets, EGFR and TGF-β, which are known to drive solid tumor growth and metastasis. Phase 2 of the study will identify an optimal biologic dose (OBD) supported by the safety, tolerability, PK, PD, and efficacy data of ficerafusp alfa. In this part, eligible subjects will be randomized to one of three treatment arms at a 1:1:1 ratio: * Arm A: ficerafusp alfa 1500 mg once weekly (QW) + pembrolizumab 200 mg every three weeks (Q3W). * Arm B: ficerafusp alfa 750 mg QW + pembrolizumab 200 mg Q3W. * Arm C (control): placebo QW + pembrolizumab 200 mg Q3W. The primary objective for the phase 3 portion is to compare the efficacy in subjects treated with ficerafusp alfa at the selected OBD in combination with pembrolizumab versus placebo with pembrolizumab. Eligible subjects will be randomized 2:1 in the treatment versus control arm during the phase 3 portion.