Sarcoid Sleuths: Investigating Unsightly Tumors

They can be unsightly and potentially disfiguring--but equine sarcoids hold a special attraction for Bruce Wobeser, DVM, of the Western College of Veterinary Medicine's Department of Veterinary Pathology. The potential for finding a more effective way to treat equine sarcoids prompted Wobeser to take another look at this ugly problem.

"In most cases, they're slow-growing tumors: some resolve spontaneously while some get worse. And then there's a proportion of equine sarcoids that just go wild and become huge," Wobeser said. "If they develop in a bad place, that can be very bad news. For example, a horse can go blind if a sarcoid grows around the eye area, and in some cases, you might even lose the horse."

Getting rid of sarcoids is challenging since tumors often come back after treatment. Even worse, conducting biopsies or surgically removing some types of tumors can trigger more rapid growth.

"If nothing else, it would be good to be able to make a prognosis so you can decide which ones to leave alone and which ones to treat," explained Wobeser. "If we could come up with other treatment options, it would be even better."

But before better therapies can be developed, scientists need to do more homework: equine sarcoids are the most commonly diagnosed skin tumors in horses around the world, but veterinary researchers know very little about them.

WCVM sarcoid tumor research
COURTESY WCVM HORSE HEALTH LINES

Histologic slides from equine sarcoid cases will supply WCVM researchers with information about the novel skin tumors.

Answering some of equine sarcoids' "unknowns" is the goal for two new research studies that are supported by WCVM's Equine Health Research Fund. Andy Allen, DVM, MVetSc, PhD, a veterinary pathologist and Wobeser's graduate supervisor, is leading the investigations in collaboration with Wobeser and Beverly Kidney, DVM, MVetSc, PhD, Dipl ACVP, a veterinary pathologist who investigates viral oncogenesis--particularly papillomaviruses.

Although equine sarcoids are diagnosed in all parts of the world, Wobeser said there seems to be regional variations in the types of sarcoids diagnosed and in the types of horses most commonly affected by the skin tumors.

"When you look through the literature, you might find one study that said mostly young horses up to seven years of age are affected, while another will suggest the average age is nine, and yet another report said that horses of any age are susceptible," explained Wobeser.

"Until now, no one has examined what's going on around here and that's what we want to do in our first study: we want to develop a 'profile' of the tumors in Western Canada."

As a first step, WCVM researchers will go through 10 years' worth of records from western Canadian veterinary diagnostic laboratories and collect information on equine sarcoid cases. Besides collecting statistics on the age, breed and sex of affected horses, the team will gather details about the tumors including the number, location and type of lesions for each case.

Another important piece of the epidemiological puzzle is whether affected horses live alongside cattle as well as other horses.

"Previous research has shown a link between equine sarcoids and two different types of bovine papillomavirus (BPV), and the disease is presumed to be infectious," Wobeser said. "Initial evidence suggests that horses living alongside cattle are at greater risk, but so far, it's not conclusive."

To explore that potential link even further, the research team will test for the presence of BPV and the disease type in archived tumor samples from the diagnostic laboratories. These findings may help researchers determine whether equine sarcoids in Western Canada have similarities to the disease identified in other parts of the world.

"In the western United States, it's almost always Type-2 BPV that's involved in equine sarcoid cases. But Type-2 BPV isn't found in European sarcoid cases: only the Type-1 BPV virus. Are these equine sarcoids the same disease? We'd like to find out."

While the disease's epidemiological profile will address some immediate questions, the study's key value is to establish a knowledge base for future sarcoid research--especially in Western Canada. Eventually, more specific studies will result in better modes of prevention and treatment for veterinarians in the field.

While sarcoids are a common problem in horses, little is known about what makes normal fibroblasts (the cells from which normal connective tissue derives) turn into sarcoid tumor cells.

A horse's body creates cells that live, die and are eventually replaced: a normal process that's essential for good health. Apoptosis, or programmed cell death, eliminates old and unhealthy cells. But when this process is absent or not working properly, problems arise. Some tumors result from the rapid division of cells, while others appear when cells just live longer than expected.

Since earlier studies have shown that sarcoids don't appear to be associated with excessive cell proliferation, the WCVM researchers will try to discover if sarcoid cells somehow escape apoptosis--or if apoptotic cells are absent in the tumors. In this second sarcoid study, the team will examine up to 90 archived tumor tissue samples that represent all six types of sarcoids seen in horses. The researchers will then use immunohistological markers to evaluate apoptosis in the tumor cells.

When veterinarians are dealing with sarcoids, one difficulty is differentiating the rapid-growing, problematic tumors from the slow growing, innocuous type. "We want to find a marker that you can stain on a slide," explains Wobeser. "Are the bad tumors expressing different markers--or do they express the same markers differently?"

If this study's findings show that the transformed cells express these markers, they may become potential targets for novel therapies or markers that veterinarians could use to predict the prognosis for treated sarcoids. That's a crucial part of dealing with sarcoids since these skin tumors often recur after treatment--or therapies can even trigger more rapid growth.

"It's sequential: first, we need to know what are sarcoids? Second, how are they growing? Third, are there tumor markers? And after that, can we use these markers for treatment?" explained Wobeser, adding that tumor markers are regularly used in human and pet cancer cases.

"If something unexpected happens along the way--as it so often does--then one possibility might lead to another," Wobeser said.


Reprinted with permission of Horse Health Lines, publication for the Western College of Veterinary Medicine's Equine Health Research Fund. Visit www.ehrf.usask.ca for more information.

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Roberta Pattison

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