Most Common Horse Cancer May Have Genetic Link

Some horses may be predisposed to sarcoid skin tumors.

The most common form of cancer in horses may have a genetic link, making some animals more susceptible than others to sarcoid skin tumors, according to a new study out of Cornell University.

The tumors present as small bumps under the skin or as scaly patches that can often be removed with methods that include surgery, laser treatment or cryotherapy (essentially "freezing off" the tumor). They're not technically fatal in and of themselves, but, in some horses, tumors that don't respond to treatment can be so aggressive they cause the animal great discomfort and loss of mobility -- enough that euthanasia may be the only option.

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Researchers with Cornell's college of veterinary medicine compared the genetic makeup of horses that had sarcoid tumors to those that did not, studying more than 50,000 places on the horse genome.

The team found regions on two chromosomes that differed in horses with the tumors compared to those without, indicating to the researchers that, at least in part, a horse's genes can determine how susceptible it is to the tumors.

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According to the study's lead author Doug Antczak, a professor of equine medicine, bovine papillomavirus (BPV) that has adapted to horses is thought to be the likely cause of most sarcoid tumors.

Why a horse does or doesn't develop the tumors has puzzled scientists, and Antczak's team's findings add to a complex picture.

"This is an example of more complicated genetics: multi-gene susceptibility," said Antczak in a statement. "More than one genetic region is associated with susceptibility to sarcoids, and they don't completely determine whether or not a horse will develop the disease once it's exposed to BPV."

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The researchers say their findings also linked immune system response with susceptibility to the tumors: One of the two chromosome regions they observed to be different in horses with tumors relates to immune function.

According to the scientists, that finding mirrors the fact that some people have a genetic susceptibility to the human papillomavirus that causes some cancers, including cervical cancer.

"That should make a light bulb go off," Antczak said. "It suggests there's a common mechanism in both species for susceptibility to tumor progression that may involve subversion of the host immune response. By studying this phenomenon in horses you can learn about human cancer and vice versa."

The team's findings have been published in the journal the International Journal of Cancer.