Equine sarcoids are the most common type of tumor found in horses. While they’re rarely malignant, they can lead to a loss of use since they’re typically located around the eyes, ears or girth area. In addition, while smaller sarcoids may easily be removed, others require more extensive treatment—from surgery, cryotherapy (tissue freezing) or drug injections to radiation, laser treatments or immunotherapy. Even then, tumors may recur.
As common as they are, there’s no definitive information on why sarcoids affect some horses and not others. There is believed to be a viral link, possibly associated to a variant of the bovine papillomavirus. Certain breeds seem more susceptible than others, indicating a possible genetic component.
The mystery led a group of international researchers, funded by a grant from the Morris Animal Foundation, to conduct a study comparing the genetic makeup of horses with and without sarcoid tumors. The team was led by Doug Antczak, VMD, PhD, the Dorothy Havemeyer McConville Professor of Equine Medicine at the Cornell University College of Veterinary Medicine, Baker Institute for Animal Health.
Researchers looked at more than 50,000 sites on the equine genome, which maps out the DNA sequence for all the chromosomes that go into building and maintaing the horse. The study used horses from the United States and the United Kingdom with 82 animals having sarcoids and 272 healthy horses acting as controls. Researchers found that genetic differences did exist between the two groups, specifically on chromosomes 20 and 22.
Since chromosome 20 is related to immune function, these findings indicate that susceptibility to sarcoids may have not only genetic but also immune-system links.
Dr. Antczak notes that this combination of virus, genes and tumor development may have relevance to a related human condition—that a common mechanism may trigger susceptibility in both species. “By studying this phenomenon in horses, you can learn about human cancer and vice versa,” he explains.
This article was originally published in Practical Horseman’s October 2016 issue.