Immunohistochemical study of a granular cell tumor on the tongue of a dog.

A granular cell tumor (GCT; myoblastoma) was diagnosed on the tongue of a 12-year-old English Pointer with clinical signs of mild oral dysphagia. The diagnosis was confirmed by histopathologic examination and immunohistochemistry. The tumor was positive for S-100 protein, but also was positive for desmin, and was only weakly positive for PAS, which is unusual for GCTs. An epithelioid type of leiomyoma (leiomyoblastoma) was considered less likely on the basis of negative staining for smooth muscle actin. Treatment consisted of surgical resection of the tumor. The animal was in excellent clinical condition 1 year after surgery. Although GCT of the tongue has been reported previously in the dog, determining the cell of origin is still problematic. Immunohistochemistry is helpful for histogenetic classification and necessary for differentiation from leiomyoblastoma.