H-FIRE comes to the rescue after a softball-sized tumor threatens the future of a horse in the show ring

Danika does circus tricks. Ask her owner, Carolyn Steppe, and she'll tell you the mare has never had a bad moment in her life — until, that is, a mass developed on the inside of her leg that grew to the size of a tennis ball, threatening to end her show career.

"She is a very social and vocal girl and loves to entertain her humans with a handful of circus tricks," Steppe said. "She never has a bad moment and is the happiest horse I've ever known — definitely my heart horse."

The journey for Danika and Steppe would lead to the Marion duPont Scott Equine Medical Center in Leesburg, one of three teaching hospitals and animal healthcare facilities of the Virginia-Maryland College of Veterinary Medicine, where Danika would receive a variety of advanced treatments, including H-FIRE, or high-frequency irreversible electroporation, a procedure that uses targeted electrical pulses to open pores in tumor cell walls.

Steppe bred and trained Danika herself, a Zweibrucker, which is a type of German warmblood. For most of the mare's career, she competed in dressage, with jumping and trail rides on the side. Then, in the fall of 2025, a sarcoid developed on Danika's right hind leg. The mass was surgically removed, but it grew back larger and more aggressive than before. 

"When it happens, you feel so hopeless," Steppe said.

For 17 years, Danika had been more than a competition partner to Steppe, who shared that she turned nearly every stranger who met her into a fan. A tumor that ate into muscle tissue and threatened her soundness wasn't just a medical problem; it was a threat to the life the two of them had built together.

A tumor the size of a softball

Sarcoids are the most common skin tumor in horses, and they have a reputation among veterinarians for stubbornness.  

Even after surgery, these masses often return, sometimes worse than when they started. That is what happened to Danika. Paul Tuck, her regular vetrinarian from Walkersville (Maryland) Veterinary Clinic,  had surgically removed the mass from the inside of her right stifle in October 2025, and the site was treated with a topical ointment postoperatively. 

Instead of healing, the surgical site reopened, and the sarcoid grew back aggressively. By the time Steppe brought Danika to the Marion duPont Scott Equine Medical Center (EMC) in November 2025, the tumor measured approximately 15 to 18 centimeters (6 to 7 inches) wide and 10 centimeters (4 inches) tall. That's roughly the size of a softball.

A second, smaller sarcoid, flat and easy to miss, had also appeared on Danika's cheek, beneath where a bridle typically sits. Systemically, Danika was a picture of health, but the sarcoids were of significant concern. 

Elsa Ludwig, an equine surgeon at the Equine Medical Center, called Steppe.

"I immediately received a call from Dr. Ludwig and was assured that she would do everything available to help Danika," Steppe said.

Extensive sarcoid treatment was necessary, but there was an additional challenge. Just weeks prior, Danika had fractured her right third trochanter, part of her hip, which ruled out general anesthesia until the bone was fully healed. Any treatment for the sarcoid would need to happen with the mare standing, and sedated, but awake.

New technology, old enemy 

Ludwig had a tool that made that possible. 

At that time, the Equine Medical Center was in the process of acquiring an H-FIRE machine, a high-frequency irreversible electroporation device that uses targeted electrical pulses to open pores in tumor cell walls. Paired with a locally injected chemotherapy drug, the technique is called electrochemotherapy, and it lets veterinarians deliver a lower, safer chemotherapy dose directly into the tumor rather than dosing the entire horse. 

Unlike traditional electroporation, which requires general anesthesia, H-FIRE can be performed standing, under sedation and local anesthesia alone, the only option available for a horse recovering from a hip fracture.

The lower chemotherapy dose matters beyond the convenience. Because the electrical pulses drive the chemotherapy drug directly into tumor cells, veterinarians can use less of it overall, which means less damage to the healthy tissue surrounding the mass and a safer recovery for the horse and the people handling her afterward. 

The plan also included something less mechanical: a piece of Danika's own tumor, frozen and later implanted beneath her skin, designed to trigger her immune system to attack the sarcoid from the inside. The technique, called autologous implantation, when combined with other sarcoid treatments, has been shown to help shrink remaining tumor tissue and guard against recurrence.

"Danika loved her visits to [the EMC]," Steppe said. "The staff were absolutely amazing and attentive towards her. From admissions to the techs and doctors, I can't give them enough credit for their compassion and expertise."

At Danika’s initial appointment, the Equine Medical Center team, which included intern Lauren Young and technician Payton Lavoie alongside Ludwig, began Danika on topical treatment to help shrink the mass while they waited for the H-FIRE machine to arrive.

The first treatment 

On Dec. 23, 2025, Danika returned for her first H-FIRE session. 

Under standing sedation, Ludwig and surgery fellow Mohamed Ali, surgically reduced the size of the large sarcoid, cutting it down to a flat base measuring 8 by 5 centimeters, roughly a third of its original size before treatment even began. Surgeons ligated the underlying tissue  before infusing the tumor bed with a chemotherapy drug, followed by delivering H-FIRE pulses across 10 sites at up to 2,200 volts. The smaller cheek sarcoid received the same combination at a single site.

Then came immunotherapy. Surgeons divided the removed tumor tissue into small frozen sections and implanted them beneath the skin of Danika's neck through four small incisions, a procedure designed to prime her immune system against any sarcoid cells left behind. 

"Immediately after her first therapy session, I could see the sarcoid shrinking," Steppe said. 

The mare went home on antibiotics and anti-inflammatories, with instructions to keep the wound clean, apply manuka honey to help it heal, and avoid handling the surgical site for 48 hours. Because of the large size of the tumor, Danika's surgery team added CO2 laser diathermy to her future visits at the EMC to help control regrowth, alongside repeated chemotherapy and H-FIRE treatments.

Steady progress, one setback

Danika returned in February 2026 for a third round of electrochemotherapy. By that visit, the tumor bed had toughened into scar-like tissue markedly different from the active fibroblastic, sarcoid Ludwig's team had first treated in December. 

Under standing sedation, the resulting scab was removed, the area was infused 30 units of chemotherapy, and Ludwig delivered another round of H-FIRE at up to 2,000 volts across six to eight sites. The cheek sarcoid, by contrast, had healed completely, with hair regrowing over the site and no thickened tissue left behind. 

Danika's team deliberately stretched the gap before her fourth visit, waiting nearly eight weeks instead of the usual four to see how the tumor would respond on its own. Steppe applied a topical sarcoid treatment ointment intermittently at home, drying the tissue into an eschar between visits and sending Ludwig weekly photos to track the mare's progress.

By April 7, 2026 — Danika's fourth H-FIRE session — the sarcoid was flat and measured just 2.9 by 5.4 centimeters. What had once been a softball-sized mass eating into muscle tissue had shrunk by more than 90 percent. 

Ludwig's team used the CO2 laser to vaporize the remaining tumor surface before infusing chemotherapy and delivering a final round of H-FIRE. As Danika's sports medicine team had already declared her hip fracture to be healed and cleared her to return to riding, Steppe was set to get back in the saddle.

"We are beyond fortunate to have a facility like the Marion DuPont Scott center within our reach," Steppe said. "The cutting-edge technology of the new H-FIRE machine and the knowledge and care of the staff is why I still have my awesome Danika." 

Why it matters beyond one horse

Fibroblastic sarcoids like Danika's carry a tougher prognosis than other sarcoid types. Most sarcoids have roughly an 80 percent chance of full resolution with treatment, but large, aggressive fibroblastic tumors are successfully treated less than 60 percent of the time, and every failed round of treatment cuts the odds of eventual success by roughly in half. 

As Danika’s sarcoid returned following the initial surgery on the farm, Ludwig's team leaned on every treatment tool available to help resolve the tumor: surgical debulking to reduce its size quickly, electrochemotherapy to attack what surgery couldn't reach, and autologous implantation to recruit Danika's own immune system into the fight. 

Combining treatments gives horses like Danika the best shot at long-term control, even when a complete cure isn't guaranteed. 

The H-FIRE machine that made Danika's treatment possible also expands what the Equine Medical Center can offer horses that, for other medical reasons, can't safely undergo general anesthesia, a limitation that has historically closed the door on aggressive sarcoid treatment for many patients. 

Veterinarians throughout Virginia and Maryland refer complex sarcoid and tumor cases to the Marion duPont Scott Equine Medical Center's specialty surgical team, and the addition of standing electrochemotherapy gives that referral network another option for horses who need it. 

Tuck, the veterinarian from Walkersville (Maryland) Veterinary Clinic, made that initial call to the Equine Medical Center once the sarcoid outpaced what could be managed on the farm. This is the kind of collaboration between local veterinarians and specialty referral hospitals that keeps horses like Danika in treatment instead of running out of options.

Danika isn't finished with treatment. She requires continued monitoring by her owner, with photo updates sent weekly to Ludwig, to help determine if there is tumor recurrence. Danika’s care team expects she may need occasional, additional H-FIRE sessions if the tumor regrows, but thus far Steppe has not noted any changes.  

Danika will also return to the Equine Medical Center to see sports medicine clinician, Gustavo Zanotto, for a final recheck of her hip fracture. But for now, the mare who was bred to perform is back doing what she loves, carrying Steppe through the same dressage movements the two of them have practiced for nearly two decades.

"She never has a bad moment," Steppe said, "and is the happiest horse I've ever known."

Danika continues to receive follow-up care at the Marion duPont Scott Equine Medical Center, in Leesburg, Virginia, which is one of three teaching hospitals and animal healthcare facilities of the Virginia-Maryland College of Veterinary Medicine, based on the Virginia Tech campus in Blacksburg, Virginia.  

For more on the hospital's equine surgical and oncology services, visit our website.