Don’t Horse Around When It Comes To Bumps: Understanding Equine Skin Tumors

March 27, 2025

Horses are known for their strength and beauty, but their skin is just as vulnerable as any living tissue. While some of the lumps and bumps commonly seen on horses are harmless, others may be cancerous tumors requiring prompt veterinary attention.

Dr. Leslie Easterwood, a clinical professor at the Texas A&M College of Veterinary Medicine & Biomedical Sciences, explains what horse owners should know about skin tumors, including common types, risk factors, and treatment options.

Lumps, Bumps And Tumors — What’s the Difference?

Not all bumps on a horse’s skin are cause for concern, but it can be difficult to tell the difference between a harmless lump and a tumor. Like tumors, noncancerous lumps can range in size; some are smooth bumps covered in normal skin and hair, while others may be ulcerated, oozing wounds.

“For example, eosinophilic granulomas are irregularly shaped skin nodules that can sometimes break open and develop into an ulcer,” Easterwood said. “They are caused by a reaction to an insect bite and are not cancerous.”

However, some lumps are more concerning. Two of the most common skin tumors in horses are sarcoids and squamous cell carcinomas (SCC), both of which can develop anywhere on the body and at any age, though they are commonly seen in older horses.

“Squamous cell carcinoma tumors are common among horses with light-colored skin, and they most often appear around the eyelids, lips, and genitals,” Easterwood said.

On the other hand, sarcoids often develop in areas that have experienced previous injury or repeated irritation, like the inner thighs, trunk, and face, especially around the eyes and ears.

Early Diagnosis And Treatment

Because skin tumors can mimic harmless lumps, identifying them early is key to preventing complications like further tumor growth or, in the case of SCC, potential spread to deeper tissue or other areas of the body.

“Early detection is very important,” Easterwood said. “Anything that looks abnormal should be seen by a veterinarian to determine the likely cause and next steps.”

Veterinarians have a variety of treatment options to manage skin tumors, depending on the type, size, and location.

“Common treatment for SCC is photodynamic dye therapy, which uses light-activated dye to target and destroy cancerous cells,” Easterwood said. “For sarcoids, surgical removal and mitomycin-c chemotherapy injections — using a cancer-fighting drug to stop tumor growth and help shrink or eliminate the mass — are common approaches.”

Preventing Skin Tumors

Skin tumors don’t have a single cause; rather, they result from a combination of environmental, genetic, and viral factors. This means that while they can be difficult to completely prevent, there are steps owners can take to reduce their occurrence.

“Skin tumors are multifactorial in causation,” Easterwood said. “For example, Halfinger horses are genetically predisposed to SCC cancers on their eyes. Sun exposure can make their tumors progress faster, but genetics got it started.”

While this can make prevention challenging, certain steps can reduce the risk of tumor development. For example, limiting sun exposure — such as UV-protective masks or keeping horses in shaded areas — can help delay SCC tumor onset.

“There is evidence that bovine papillomavirus, a disease transmitted to horses by flies, contributes to sarcoids, so controlling fly exposure might help reduce the risk,” Easterwood said.

For all kinds of skin tumors — as well as noncancerous lumps — regular skin checks and prompt veterinary care are simple steps that can help catch small bumps before they become big problems.

Staying proactive and informed can make a big difference in horses’ comfort and health. By watching out for any suspicious lumps and bumps, owners can keep their horses happy, healthy, and ready to gallop into the future.

Pet Talk is a service of the College of Veterinary Medicine & Biomedical Sciences, Texas A&M University. Stories can be viewed on the web at vetmed.tamu.edu/news/pet-talk. Suggestions for future topics may be directed to vmbs-editor@tamu.edu.