What is squamous cell carcinoma? Squamous cell carcinoma (SCC) is the most common tumor of the equine eye. It can occur on the cornea, eyelids, third eyelid, and conjunctiva. Horses with lack of pigmentation of the eyelids or around the eye are at increased risk for the development of SCC. The at-risk breeds include Appaloosas, Quarter horses, and Paints. Other breeds, such as Thoroughbreds, Haflingers, and draft horses (Belgians, Shires, and Clydesdales) have an increased p