A Global Study of Volrustomig (MEDI5752) for Participants With Unresected Locally Advanced Head and Neck Squamous Cell Carcinoma Following Definitive Concurrent Chemoradiotherapy

The main purpose of this study is to assess the efficacy and safety of volrustomig compared to observation in participants with unresected locally advanced head and neck squamous cell carcinoma (LA-HNSCC) who have not progressed after receiving definitive concurrent chemoradiotherapy (cCRT).

Inclusion Criteria: * Histologically or cytologically documented locally advanced squamous cell carcinoma of the oropharynx, hypopharynx, oral cavity, or larynx with no evidence of metastatic disease (i.e. M0). * Confirmed unresected Stage III, Stage IVA or IVB according to the eighth edition of the American Joint Committee on Cancer (AJCC) staging manual (tumor, node, metastasis (TNM) staging system). * Participants will have completed definitive concurrent chemoradiotherapy (cCRT) with curative intent prior to randomization. Exclusion Criteria: * Histologically/cytologically confirmed head and neck cancer of any other primary anatomic location in the head and neck not specified in the inclusion criteria including participants with squamous cell carcinoma of unknown primary or non-squamous histologies (eg, nasopharynx or salivary gland). Participants with \>1 primary tumors are not eligible for the study. * Participants with any of the following: 1. LA-HNSCC that was resected before definitive cCRT 2. LA-HNSCC that was treated and is recurrent at the time of screening * Participants who have received radiotherapy (RT) alone as definitive local therapy for LA-HNSCC.