A case of glomus tumor in a dog.

A subcutaneous mass at the digit of the left-hind limb of a 12-year-old, male mongrel dog was examined. A white firm mass, approximately 1 x 2 cm in diameter, was excided surgically. Histopathologically, the mass formed multiple nodules consisting of mixed proliferation of round epithelioid cells arranged in cord or sheet-like structures and small spindle cells forming loose irregular bundles. The epithelioid cells often showed proliferation around the blood vessels. A few giant cells scattering in the neoplastic foci were observed. The neoplastic cells were positive for alpha-smooth muscle actin and vimentin, and were negative for cytokeratin (AE1/AE3), desmin, factor-VIII related antigen, S-100 protein, and neuron specific enolase. On the basis of these findings, this tumor was diagnosed as glomus tumor. Since the present neoplasm had neither recurrence nor distal metastasis during the 12 month after surgical resection, the biological natures of the present neoplasm are supposed to be benign.