A new clinical trial targeting sarcoids — the most common and persistent equine skin tumor — could advance noninvasive tumor therapies for both animals and people.
There is no “one-fix-for-all” solution for sarcoids, said Sophie Bogers, an assistant professor of large animal surgery. Many of them require chemotherapy or invasive surgery. But she wants a better solution.
Elsewhere on the Virginia Tech campus, in biomedical engineer Eli Vlaisavljevich's lab, a colleague has what may be that better solution: A technology called histotripsy that uses focused ultrasound to produce a bubble cloud that can break down tumor tissue.
A team of engineers and veterinarians are working together to develop a wearable device that would allow histotripsy to be performed safely on horses. This spring, their system got its first real test on a horse named Pea, a 9-year-old Hanoverian mare who had a tumor on her belly.
“She was really good about it,” said Bogers, who led Pea's treatment. “She just stood there, was very happy. She didn't seem to feel or dislike the histotripsy.”
Pea's case was the first live test in a Virginia-Maryland College of Veterinary Medicine clinical trial trying to answer whether this sound-wave technology could treat sarcoids, the most common and hardest-to-beat skin tumor in horses.
Researchers don't yet know whether histotripsy can reliably keep a sarcoid from coming back, but they do know that at least one horse can tolerate the treatment standing and awake, with no apparent ill effects.
A tumor that won't quit
Sarcoids are the most common skin tumor in horses, and notoriously hard to eliminate.
When one keeps recurring, especially in a spot like an eyelid or a girth line, owners can cycle through procedures, wound care, and cost for months or years with no resolution.
“In some cases for large sarcoids, people find the management of the sarcoid becomes too much, and they elect euthanasia,” Bogers said.
Sarcoids form when bovine papillomavirus meets a horse's own genetic susceptibility.
“Fibroblastic sarcoid is basically a fleshy mass that horses get on their skin,” Bogers said. The worst look like big red blobs. Left alone, they ulcerate, bleed, and attract flies.
Standard treatment is surgical removal, often paired with chemotherapy, but a lot of sarcoids sit in spots too big or too awkward to treat surgically. Chemotherapy carries risks for the people delivering it, especially in a farm setting.
Why sound waves
Histotripsy was developed to treat cancer in people at the University of Michigan. It reached Virginia Tech through Vlaisavljevich, Bill and Lavinia Hall Faculty Fellow in the College of Engineering. His lab has spent years refining the technology for human liver, kidney, and pancreatic tumors, work that helped earn Virginia Tech recognition as one of 12 Focused Ultrasound Centers of Excellence in the world.
Joanne Tuohy, associate professor in surgical oncology at the veterinary college, had already been using histotripsy against cancer in dogs, and Bogers said that's what made horses feel like an obvious next step.
Ultrasound is a tool equine vets already trust, Bogers said. “We do ultrasound on horses all the time, and equine practitioners are very comfortable with ultrasound,” she said.
She wants a device portable enough to carry on a truck so a sarcoid can be treated the day it's found instead of months later.
“The more horses that have sarcoids treated early, the less management problem that they'll be, the less morbidity there'll be from having these big lesions,” Bogers said.
Engineers are now building a version of the device powerful enough to deliver stronger energy while staying portable.
Along the way, the team also solved a horse-specific problem. Histotripsy in people relies on a water bath to carry the sound waves, which doesn't work on a standing horse. The fix was a solid, gel-based coupling pad, the kind used for routine ultrasound.
Pea's day
Pea's owner, Kelly Kuykendall, wasn't looking for a clinical trial. Her longtime veterinarian noticed the small growth on Pea's abdomen and called around for surgical pricing.
“Somehow it circled around to, oh my gosh, we have this study,” Kuykendall said. “My vet called me back within a couple hours and she said: 'I've got great news. If you want to participate in a study, you can get this whole entire thing removed for free.' ”
“It's super cool that we get to help advance science and try to be at the top of the new technologies that are up and coming,” Kuykendall said.
She hauled the mare up from North Carolina. Pea stayed overnight, and surgeons removed the tumor the next morning. By lunchtime, she was headed home. “It was just everything was easy peasy,” Kuykendall said.
She hadn't realized, until she got there, that Pea would be the first horse in the trial treated with histotripsy while awake.
“I was like, oh my gosh, that's incredible,” Kuykendall said. “I'm not worried about that, I'm just thrilled. I think it's so cool that we're the first people that are coming in to do this.”
Bogers called the surgery a curative excision, and the team confirmed tumor destruction with both the handheld probe and the robotic positioning device.
What's next
It's an early, encouraging sign, but not yet full proof the treatment works. Bogers needs four more horses to complete this phase of the study.
Bogers is especially interested in hearing from referring veterinarians. “I would really like referring vets to know about this,” she said. She's willing to travel to meet a veterinarian and horse on-site and walk through the surgical technique together, in exchange for access to the tumor tissue for research.
“I would say to go ahead and take care of it as early as you can,” Kuykendall said, reflecting on Pea's case. “I would highly encourage anybody to sign up for it, because it's beneficial for so many reasons. It's a win-win across the board for horse owners, and for doctors and advancement of equine welfare, and everything else.”
Source: VirginiaTech