Picture Prognosis

A 47-year-old man with a 9-month history of a progressively enlarging non-pigmented ulcerative oral lesion involving the hard palate and maxilla presents with tooth mobility, intermittent bleeding, and bilateral cervical lymphadenopathy. Initial biopsy suggests a spindle cell malignancy. Immunohistochemistry shows S-100, SOX10, and Melan-A positivity, with cytokeratin negativity. He later develops brain metastases despite pembrolizumab. What’s Your Diagnosis?