Sarcoid within the oral cavity of a horse.

Equine sarcoids are common skin tumors that are thought to be caused by cross-species infection by bovine papillomaviruses (BPV). A 16-year-old horse developed a 1cm diameter mandibular gingival mass opposite the right second premolar tooth (406) and a 2cm diameter mass close to the commissure of the lips on the same side of the mouth. The right cheek was diffusely thickened. Histology of the smaller mass revealed a proliferation of mesenchymal cells covered by hyperplastic epithelium that formed thick rete pegs. BPV2 DNA was amplified from the mass. Although the mass had been incompletely excised, there was no recurrence after 5 months. The histological features and detection of BPV2 DNA is consistent with a diagnosis of equine sarcoid. Sarcoids have not previously been reported in the oral cavity of horses. It is hypothesized that trauma to the mouth may have been important for sarcoid development. Additionally, different BPV types may have variable ability to infect the gingiva. While rare, sarcoids are a differential for an oral mass in a horse.