A Study of Dostarlimab vs Placebo After Chemoradiation in Adult Participants With Locally Advanced Unresected Head and Neck Squamous Cell Carcinoma

Required: PD-L1 (CD274) positive tumor status

PD-L1 positive tumor status

Required: CDKN2A p16 immunohistochemistry testing required

If the primary tumor site is oropharyngeal carcinoma, the participant must have p16 immunohistochemistry (IHC) testing.

Must have received: cisplatin plus radiotherapy (cisplatin) — CRT with curative intent

completed cisplatin plus radiotherapy (termed "CRT" in this protocol) with curative intent

Cannot have received: radiation therapy, systemic therapy, targeted therapy, or surgery not considered part of CRT

Has received prior radiation therapy (RT), systemic therapy, targeted therapy, or surgery for management of head and neck cancer not considered part of CRT

Cannot have received: induction chemotherapy

Participants receiving induction chemotherapy are excluded

Cannot have received: CRT combinations with components other than cisplatin and RT (e.g., experimental agents, including radiosensitizers/radioprotectants, cetuximab) (cetuximab)

CRT combinations with components other than cisplatin and RT (e.g., experimental agents, including radiosensitizers/radioprotectants, cetuximab) are not eligible

Cannot have received: anti-PD-1/PD-L1/PD-L2 or co-inhibitory T-cell receptor therapy

Previous treatment with anti-PD-1, anti-PD-L1, or anti-PD-L2 agent or an agent directed to another stimulatory or coinhibitory T-cell receptor [e.g., Cytotoxic T-lymphocyte associated protein 4 (CTLA4), OX-40, CD137]