Phase II Study of Nivolumab in Combination With Radiation Therapy as Definitive Treatment for Patients With Locally Advanced, Unresectable Head and Neck Mucosal Melanoma.

Inclusion Criteria: * Age ≥ 19 years * Histologically or cytologically confirmed mucosal melanoma of head and neck * Locally advanced and unresectable * No previous chemotherapy for purpose of palliation * ECOG performance status of 0\~2 * Measurable lesion per RECIST 1.1 criteria * Be willing to provide fresh tissue for biomarker analysis, and, based on the adequacy of the tissue sample quality for assessment of biomarker status. Repeat samples may be required if adequate tissue is not provided. Newly obtained endoscopic biopsy specimens are preferred to archived samples and formalin-fixed, paraffin-embedded (FFPE) block specimens are preferred to slides. * Newly-obtained is defined as a specimen obtained up to 6 weeks (42 days) prior to initiation of treatment on Day 1. Subjects for whom newly-obtained samples cannot be provided (e.g. inaccessible or subject safety concern) may submit an archived specimen. * Collection of an archived tissue sample will also be requested (where available) to support evaluation of the clinical utility of biomarker assessment in newly obtained vs. archived tissue samples; however, a subject will not be precluded from participating in the study if an archived tissue sample is not available for collection or is otherwise insufficient for analysis. * Adequate marrow, hepatic, renal and cardiac functions: Serum aspartate transaminase (AST) and serum alanine transaminase (ALT) ≤ 2.5 x upper limit of normal (ULN), or AST and ALT ≤ 5 x ULN if liver…