Distinctive tumour of the tongue in 3 horses

Tumours arising from the dorsal surface of the tongue occurred in 3 horses from 14 to 23 years of age. Tumours were surgically excised at a referral hospital (1 case) and on the farm (2 cases) and submitted for histopathology. All tumours were multilobular and composed of vaguely nested, bland, oval to slightly elongated cells with an infiltrative growth pattern. Mitotic activity was not detected. Immunohistochemical studies found that tumour cells were often positive for S-100 and cytokeratin and occasionally positive for vimentin. Tumour cells were negative for glial fibrillary acidic protein, neuron specific enolase, synaptophysin, muscle actin and chromogranin A. Follow-up obtained from 7 months to 2 years following tumour removal indicated no evidence of regrowth or metastasis. The origin of these distinctive tumours is not clear but the immunohistochemical profile suggests the possibility of origin from lingual taste buds. These cases and review of the literature indicate that successful surgical excision of tongue tumours can be performed by practitioners in private practice as well as by surgeons at referral hospitals.