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May 18, 2017 – No species of animal is immune to the ravages of cancer. Cancer is found in diverse animal species, from mice to sharks. Horses are no exception. They share many of the same cancers seen in other animals as well as people; cancers which can be devastating for horses and their owners.

Treating large animals with cancer can be difficult. For many years, equine veterinarians tended to take a passive approach to horse cancers, but this practice is being called into question.

“For too long veterinarians have advised watchful waiting as a treatment option for cancer in horses,” said Dr. Jeffrey Phillips, a Morris Animal Foundation-funded researcher and Assistant Professor of Immunology and Oncology at Lincoln Memorial University-College of Veterinary Medicine. “This has never made sense to me. Would we ignore a mass on ourselves?”

Morris Animal Foundation has a long history of funding studies looking into the various aspects of cancer biology in many animal species, including horses. In the last 10 years, we’ve invested just over $150,000 in seven studies focused specifically on squamous cell carcinoma, melanoma, and sarcoid tumor biology and treatment.

One of the Foundation’s most promising studies recently was completed by Dr. Phillips. His research focused on the treatment of melanoma in horses, and he proposed a daring solution – use the canine melanoma vaccine in horses with the disease. Dr. Phillips devised a treatment protocol for horses, and his study was a stunning success. Dr. Phillips achieved dramatic reduction in tumor size in the majority of horses, and arrested tumor growth in the remaining patients. Many of the original study horses continue to thrive in spite of their cancer. Dr. Phillips’ results are providing hope to thousands of horses and their owners who struggle with this debilitating cancer.

Melanoma is one of the most common types of skin tumors found on horses. This form of cancer is especially prevalent in grey horses, reaching an incidence rate as high as 80 percent. The tumors often are advanced by the time they are diagnosed, and result in prolonged and significant discomfort for affected horses.

Squamous cell carcinoma is the most common cancer of the eye in horses. Experts suspect that because horses spend so much time outdoors, they are exposed to high levels of UV light, which is a risk factor for this type of cancer. Squamous cell carcinoma can be painful for the horse, and is difficult to treat. Ultimately, this devastating tumor can lead to removal of the eye and euthanasia in some horses. Foundation funded researchers recently found a genetic risk factor for this type of cancer in Haflinger horses, an important first step in developing improved diagnostic tests for this important cancer.

Although horses share some skin cancers with other species, sarcoids, the most common equine tumor, are found only in equids. Sarcoids are caused by a virus and certain horses and breeds of horses are more susceptible than others. The disease is a major animal health problem worldwide, and affects not only horses but also donkeys and zebras. Although the majority of sarcoids are not malignant, they tend to grow around the eyes, ears and girth, causing irritation to the horse.

Cancer is a frightening disease for owners of companion animals large and small. For horse owners, what was once a dismal landscape is just a little bit brighter thanks to the Foundation’s efforts in discovering new ways to treat cancer in horses.