Squamous cell carcinoma is one of the most common periocular tumors in horses, specifically horses located in areas of intense sunlight or high altitude. Non-pigmented regions of the skin are susceptible to the development of this tumor. The tumor may involve the eyelids, third eyelid, cornea or the tissues surrounding the eye itself. Appaloosas, color-dilute breeds, Belgians and other draft horses are particularly susceptible to development of this tumor.
A horse with an early squamous cell carcinoma lesion can be seen with a reddening, roughening or ulcerated area, along with increased tearing of the eye. The tumor soon develops into a small pink or red mass, which if left untreated, can enlarge and spread around and behind the eye, to the skull, sinuses of the skull, brain and to other parts of the body. Squamous cell carcinoma can be diagnosed in its earliest stages by a biopsy of the lesion, which can be performed by your veterinarian or veterinary ophthalmologist. Treatment and prognosis of squamous cell carcinoma vary with the location, size, and the extent of the tumor. Treatments may involve surgical removal, freezing or heating, radiation, laser ablation, immunotherapy, chemotherapy or a combination of the above. In some of these cases, the tumor becomes inoperable and the outcome can be devastating. There is potential for recurrence of the tumor despite the type of treatment used, and additional treatments may be necessary. The prognosis for horses with squamous cell carcinoma is usually good if the tumor is small and can be completely excised. If the tumor is large and extensive or involves the eyelids or space behind the eye, the prognosis may be poor.
The following are recommendations to minimize your horse’s risk of squamous cell carcinoma: avoid peak sun exposure between 10 a.m. and 3 p.m.; provide protection of the eyes from insects, dust, and wind by using an ultraviolet protective mask, sunscreen and ﬂy repellent.