Neoplasia of the mouth and lips other than viral papillomas can occur in large animals. The most common types include melanomas, sarcoids (see ), and squamous cell carcinomas.
A large, aggressive sarcoid on the lower lip of a horse.
Courtesy of Dr. Jan Hawkins.
In gray horses, melanomas can develop and infiltrate the commissures of the mouth and cause hard, thickened, tumorous plaques that might not be detected until well advanced. Verrucose, fibroblastic, and sessile or flat forms of equine sarcoids can involve the mouth and lips.
Squamous cell carcinomas are not uncommon in white-skinned horses, including Paint and Quarter Horses. Inflammatory masses can mimic neoplastic masses; habronemiasis is the most common. Histological examination should be performed to differentiate between inflammatory and neoplastic masses and obtain a definitive diagnosis.
Removal of oral and lip melanomas using a carbon dioxide laser should be considered. Complete removal is not necessary for a successful outcome. In addition, some horses might respond to oral cimetidine therapy.
Surgical resection of sarcoids can be performed successfully with a carbon dioxide laser. Along with laser resection, intratumoral administration of cisplatin may be considered, to lessen the chances of recurrence.
Cryosurgery is another acceptable method of treating squamous cell carcinomas.
Because they are invasive, squamous cell carcinomas can be difficult to treat. One treatment method that can be successful is surgical debulking with a carbon dioxide laser, followed by the injection of cisplatin into the tumor.
No matter how oral squamous cell carcinomas are treated, the prognosis is guarded to poor. (Also see Tumors of the Skin and Soft Tissues.)
For More Information
Auer JA, Stick JA, Kümmerle JM, Prange T, eds. Equine Surgery. 5th ed. Saunders; 2019.
Also see pet owner content regarding disorders of the mouth in horses.
