Primary cutaneous plasmacytomas in the dog and cat

The clinical, light microscopic and ultrastructural features of twelve cases of primary cutaneous plasmacytomas are described (11 dogs and one cat). The tumours were solitary in all but one case, tended to grow rapidly but did not recur after removal and had a predilection for the feet, lips and ear canal. Primary cutaneous plasmacytomas should be considered in the differential diagnosis of round cell tumours of the canine and feline skin. They appear to be benign tumours unrelated to the malignant disease of myelomatosis.