Multiple cutaneous histiocytomas in a cat

A 15-year-old domestic long haired cat developed nodular cutaneous masses o ver the right shoulder that were removed surgically. Similar masses develop ed in multiple cutaneous sites over the following three years. In each case , the lesions were characterized by diffuse dermal infiltration by histiocy tic cells with a low mitotic rate and evidence of epidermotropism. The neop lastic population uniformly expressed class II molecules of the Major Histo compatibility Complex, but did not express the T and B lymphoid markers CD3 and CD79. Perivascular aggregates of CD3(+) T lymphocytes were located at the deep margins of the tumour nodules. The clinical, histopathological and immunohistochemical features of these tumours are consistent with cutaneou s histiocytoma. This tumour has not been previously well-documented in the cat.