SCC

Squamous cell carcinoma (SCC), a type of skin cancer that commonly occurs on white-skinned areas of horses, can be difficult to treat. That’s why Leslie Easterwood, MA, DVM, a clinical assistant professor at the Texas A&M College of Veterinary Medicine & Biomedical Sciences, in College Station, said early detection and treatment are key.

She said SCC most commonly occurs at mucocutaneous junctions, such as the eyes, nose, sheath, vulva, and rectal sphincter. Although SCC has some genetic predispositions, sun exposure can also accelerate the disease.

Easterwood added that SCC also can develop if the horse has prolonged liver disease or if the horse has had a thermal (i.e., burn) injury. Long-term exposure to toxic plants can also increase the risk of liver dysfunction and, thus, lead to SCC on the affected white skin.

Early SCC lesions typically look like ulcerated erosions of the skin or sun burning. These lesions can develop into tumors and spread to other areas of the body, including the lymph nodes and sinuses.

If you think your horse might be developing a SCC tumor, work with your veterinarian to implement care immediately.

“SCC tumors tend to enlarge and damage surrounding tissue,” Easterwood said. “As the tumors enlarge, they invade larger areas, and this makes removal more difficult. Eyelid lesions are particularly important to catch and treat early so that we can maintain enough eyelid tissue so that the horse will be able to blink and lubricate the eye. In advanced cases, we sometimes have to remove the eye, even though it is not affected by the tumor, because we do not have enough functioning eyelid to maintain lubrication of the globe.”

There are a variety of ways to treat SCC; the ideal treatment for each case is based on many factors, such as the location of the tumor and the risk of the tumor spreading, Easterwood said. Surgery, chemotherapy, and cryotherapy are some of the traditional options.

Additionally, veterinarians at the Texas A&M Veterinary Medical Teaching Hospital (VMTH) have been using photodynamic dye therapy (PDT), which involves removing of most of the tumor and injecting dye into the affected area. The dye is then activated by exposure to a therapeutic light, which causes the release of molecules that kill the remaining cancerous cells.

“To date, we have performed about 100 PDT procedures at the VMTH and have had overwhelmingly positive results,” Easterwood said.

There are also ways to help prevent SCC.

“Any decrease in sun exposure is likely helpful,” Easterwood said. “Face masks with UV (ultraviolet) protection, SPF (sun protection factor) protective lotions, and limited turnout during daylight hours are all ways to decrease SCC risk.”

Horses that have had SCC tumors in the past are more likely to develop them again. It’s best to always keep an eye on your horse and report any skin abnormalities to your veterinarian.