With summer under way, many horse owners begin the annual campaign to protect their white-faced horses from the sun. Sun damage causes many different problems—issues ranging from a simple case of sunburn all the way to skin cancers. In fact, periocular squamous cell carcinoma (PSCC)—the most common cancer affecting the eye and ocular structures of the horse—is directly linked to sun exposure. It can be painful and difficult to treat, so forewarned is forearmed! Prevention is the best way to avoid facial cancer.

PSCC is a malignancy that commonly affects horses on the cornea, third eyelid, or eyelid. Predisposing factors include breed (Belgians, Paints, and Appaloosas most commonly), poor pigmentation (light-colored skin), and exposure to ultraviolet light at high altitudes or frequent sun exposure.

Prevent Sunburn and Photosensitivity
How do you know if your horse is getting sunburned? It looks just like sunburn on your own skin: pink or red skin with blistering, cracking and peeling. Horses with large white patches on their faces or heads are at higher risk, but white socks or bellies can even allow the sun to burn. If the skin underneath the white hairs is pink, be proactive to prevent sunburn in that area.

Some industry groups report that certain weeds may also increase photosensitivity in horses. These include white clover, ragwort, St. John’s wort, field bindweed and buckwheat. These weeds contain alkaloids that can cause liver damage and, subsequently, high sensitivity to the sun. Maintaining a weed-free pasture can avoid exposing a horse to additional risk.

New Treatment
If your horse develops PSCC, there is hope. Researchers at the University of Missouri have developed a new treatment approach to PSCC, and preliminary results suggest that it may be more effective than current treatments, require fewer treatments/shorter hospital stays, and result in the preservation of eyelid function.

With funding from the Denver-based Morris Animal Foundation, Dr. Elizabeth A. Giuliano at the University of Missouri has developed a new therapy consisting of surgical resection and local photo-dynamic therapy.

Giuliano and her team first surgically resect the tumor and then apply laser light immediately after injecting a photodynamic drug into the tumor bed. Results from the study thus far show that the combined therapy prevents tumor recurrence, requires fewer hospital visits, and has better cosmetic outcome for horses with cancer.

Long-term, the big-picture benefits to the research are that the treatment may work on this type of tumor in other locations on your horse and also in other species.

Case Example
Dixie, a 17-year-old gray American Saddlebred horse, was the first horse to receive the treatment after her owner, Rose Pasch of Cuba, Missouri, and her veterinarian noticed that Dixie’s eye was irritated while participating in a parade. The cause was a troublesome growth. Although it was removed the next day, the growth returned.

"It kept getting bigger, and she’d keep her eye closed all the time, and it would water," Pasch said. "It was hurting her."

Pasch took Dixie to Dr. Giuliano, who was conducting a pilot clinical trial for PSCC treatment.

"Because the skin on the face of the horse tightly adheres to the underlying bone, we can’t do certain reconstructive procedures," Dr. Giuliano says. "Without retaining the eyelid, it is virtually impossible to save the eye." Losing an eye is disastrous for horses, who rely heavily on sight, especially in work and performance situations.

"Dixie was the very first horse I treated with this therapy," Dr. Giuliano says. "I did have to treat her twice, but she’s been cancer-free for five years." For the pilot study, Dr. Giuliano treated 20 horses with the new therapy with encouraging results. She received a second grant to further study the treatment and is currently evaluating PSCC’s ability to inhibit tumor recurrence over time.

Thanks to Dr. Giuliano’s research, and other equine health projects being funded by Morris Animal Foundation, the hope is that Dixie—and horses like her—will march on for many years to come.