Immunohistochemistry was required to determine histogenesis and comprised diffuse p16, SOX10, pan melanoma positivity, mild preferentially expressed antigen in melanoma (PRAME) expression, and negativity for epithelial, neuroendocrine, hematopoietic, and other lineage markers, while Ki-67 was positive in 50% of tumor nuclei. The gene discussed is MKI67; the disease is neoplasm.