Laryngeal squamous cell carcinoma and papilloma associated with Equus caballus papillomavirus 2 in a horse

A case of laryngeal squamous cell carcinoma (SCC) and squamous papilloma in a 19-year-old Thoroughbred stallion is described. The animal exhibited severe wheezing caused by laryngopharyngeal stenosis. Histological examination identified laryngeal, laryngotracheal, and guttural pouch tumor masses consisting of areas of SCC. In the epiglottic lesion, the overlying epithelium was replaced by papilloma cells, and superficial cells frequently had nuclear inclusion bodies that expressed oncoprotein E6, which is characteristic of high risk human papillomaviruses. The papillomatous epithelium was continuous with epithelium composed of SCC cells. Equus caballus papillomavirus 2 (EcPV2) DNA was detected in the guttural pouch tumor. These findings suggest that laryngeal SCC and papilloma are a continuum of EcPV2-induced neoplastic lesions in horses.