Epithelioid malignant peripheral nerve sheath tumour in a dog

An unusual morphological variant of malignant peripheral nerve sheath tumour, in which the cells exhibited a predominantly epithelial morphology, was diagnosed in a dog. The animal had a history of progressive ataxia. Post-mortem examination revealed an infiltrative growth in the sublumbar region, encroaching on the L1 and L2 vertebral bodies; additional masses were observed in the kidneys, liver and lungs. Histologically, the subcutaneous mass was composed of a dense population of spindle-shaped cells arranged in fascicles. The internal masses were composed of epithelioid cells arranged in a nodular pattern. Immunohistochemically, the spindle-shaped cells of the subcutaneous mass were positive for S-100, and the epithelioid cells of the internal growths exhibited weak S-100 immunoreactivity.