A Study to Assess Adverse Events, Change in Disease Activity and Optimal Dose of Intravenous (IV) Telisotuzumab Adizutecan With IV Pembrolizumab for First-Line Treatment of Adult Participants With Recurrent or Metastatic Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the seventh most common cancer worldwide with an annual incidence of approximately 700,000 cases. This study aims to evaluate the change in disease activity and optimal dose, and optimal dose of telisotuzumab adizutecan in combination with pembrolizumab as first-line treatment in participants with recurrent or metastatic head and neck squamous cell carcinoma. Telisotuzumab adizutecan is an investigational drug being developed for the treatment of recurrent or metastatic HNSCC. Participants are placed into 3 treatment groups called treatment arms. Each group receives a different treatment. Adult participants diagnosed with recurrent or metastatic HNSCC who have not received prior systemic therapy for advanced disease and whose tumors express c-Met protein will be enrolled. Approximately 180 participants will be enrolled in the study at sites worldwide. Participants will receive intravenous doses of telisotuzumab adizutecan with intravenous pembrolizumab, or standard of care (SOC) chemotherapy with pembrolizumab. Participants will receive treatment as part of a 38 month study duration. There may be higher treatment burden for participants in this trial compared to their standard of care due to study procedures. Participants will attend regular visits every 3 weeks during the study at a hospital or clinic. The effects of the treatment will be checked by medical assessments, blood tests, checking for side effects and completing questionnaires.

Inclusion Criteria: * Histologically or cytologically confirmed diagnosis of recurrent or metastatic head and neck squamous cell carcinoma that is considered incurable by local therapies. * Eastern cooperative oncology group (ECOG) performance status must be \= 25% tumor cells. * Must have measurable disease per response evaluation criteria in solid tumors (RECIST) v1.1. * Must have had no prior systemic therapy for recurrent or metastatic head and neck squamous cell carcinoma (HNSCC). Exclusion Criteria: * Have history of interstitial lung disease or pneumonitis that required treatment with systemic steroids, or any evidence of active interstitial lung disease or pneumonitis on screening chest computed tomography (CT) scan. * Have any major, life-threatening conditions. * Life expectancy should be at least 3 months.