Oral metastatic melanoma with neurosarcomatous transformation in a dog

Abstract

A 16-year-old male terrier dog was presented with a history of progressively growing ulcerated and slightly pigmented oral masses on the rostral mandible. Microscopically, the tumor composed of two different components. One component was conventional malignant melanoma including epitheloid or spindle-shaped components with/without melanin pigment. The other component was typical palisades (Verocay bodies) and pseudopalisades, with no melanin pigment. Immunohistochemical analysis revealed that the tumor was positive for vimentin, Melan-A, NSE, and GFAP, and negative for HMB45, S100, MBP, desmin, SMA, pan-cytokeratin. Melan-A reactivity was limited to the upper conventional melanoma areas. Nuclear palisading and pseudopalisading structures were positive for vimentin, NSE, GFAP whereas negative for other antibodies. Metastatic lymph node displayed spindle cell melanoma, with immunoreactivity for vimentin and Melan-A. The diagnosis was typical of oral malignant melanoma including nuclear palisading and pseudopalisading components, suggesting neurosarcomatous differentiation in a dog.