Fear not: A variety of therapies are available to treat this common eye tumor.

Most owners are diligent about giving their horses a once-over for scrapes and swellings while grooming. This includes checking the eyes for subtle changes and early indicators of problems. Squamous cell carcinoma (SCC), for instance, is something an owner might notice; it is one of the most common cancerous tumors of the equine eye. Fortunately, with early intervention it’s treatable.

Amber Labelle, DVM, MS, Dipl. ACVO, a veterinary ophthalmologist at WestVet in Garden City, Idaho, says the most common locations for periocular (around the eye) SCC include the eyelid skin, third eyelid, and the limbus (the junction between the cornea–the clear surface of the eyeball–and the conjunctiva that covers the white of the eye).

“On the eyelid, SCC generally appears as a pink mass, often ulcerated or bloody,” she explains. “On the third eyelid or at the limbus it generally appears as a pink proliferative mass that can distort the tissues or create a mass on the surface of the eye. The tumor is generally pink or red in color.” The affected eye might squint or emit a yellow or white discharge; this is typically what the owner notices first.

Brendan Mangan, DVM, MS, Dipl. ACVO, an ophthalmologist at Affiliated Veterinary Specialists, in Gainesville, Florida, says SCC lesions and the adjacent tissue typically appear more red and inflamed than the surrounding normal tissue.

Causes and Risk Factors

Some horses are more vulnerable to SCC than others. “There are several known risk factors,”