Sarcoids in Horses: What They Look Like and the New Sound-Wave Trial

Sarcoids in horses and the new sound-wave trial

Sarcoids in horses are the most common skin tumor horses get: flat hairless patches, warty crusts, firm lumps or raw fleshy growths linked to bovine papillomavirus in horses with a genetic susceptibility. They rarely spread to internal organs, but they are famously stubborn, and on Oct 14, 2026, The Horse reported a trial testing whether focused sound waves can destroy them.

The trial is at the Virginia-Maryland College of Veterinary Medicine at Virginia Tech. It's testing histotripsy, a noninvasive method that uses focused ultrasound to create a cloud of tiny bubbles that breaks down tumor tissue. The method was first developed for human cancer at the University of Michigan, and a Virginia Tech engineering lab has refined it for liver, kidney and pancreatic tumors in people.

What happened with the first horse

• The first patient was Pea, a 9-year-old Hanoverian mare with a sarcoid on her belly, treated in spring 2026.
• She was treated standing and awake. Dr. Sophie Bogers, an assistant professor of large animal surgery who led the treatment, said the mare stood calmly and didn't seem to feel or mind it.
• In Pea's case, surgeons removed the tumor the next morning and confirmed the tissue had been destroyed. Pea went home by lunchtime.
• For horses, the team swapped the water bath used in human treatment for a solid gel pad, and a more powerful portable version is in development.

The researchers are careful about what this means. It's an encouraging first step, not proof, and it's too early to know whether histotripsy prevents sarcoids from coming back.

What does a sarcoid look like on a horse?

Sarcoids vary so much that even vets sometimes need a second look. Vets recognize six types, and many horses carry a mix, so one horse can have a flat patch by the eye and a lump in the groin.

The other two are mixed (two or more types together, which is very common) and malevolent. Malevolent sarcoids are rare and aggressive, spreading through the skin and sometimes along lymph vessels, and they need specialist attention fast.

Where sarcoids tend to show up

They can appear anywhere, but favorite sites include:

• The head: eyelids, ears, lips and around the mouth
• The underside: chest, belly, sheath or udder
• The groin and inner thighs
• The legs and neck
• Old injuries, scars and places where tack rubs

A sarcoid under the girth, saddle or bridle can make a horse unrideable, so location matters as much as size.

Lumps that can look similar

Not every lump is a sarcoid. Proud flesh on a healing wound, warts (papillomas) on young horses, melanomas in gray horses and simple skin infections can all fool an owner. That's exactly why a vet should look before anyone treats. For other common skin problems, see our guide to rain rot.

Why sarcoids come back after being disturbed

Here's the frustrating part: a sarcoid is usually bigger than what you see. The virus can sit silently in normal-looking skin around the lesion, and trauma seems to wake it up.

• Injury is a trigger. Sarcoids often start at wound sites, and tack rubs or partial removal can push a lesion toward a more aggressive form.
• Even a biopsy carries risk. The Merck Veterinary Manual warns that sampling a sarcoid can trigger rapid growth, so many vets diagnose by appearance and only take tissue when they plan to remove the whole thing.
• Recurrence is common. Merck cites recurrence rates of 15% to 82% after surgery alone. In one New Zealand study of 49 cases, about a quarter came back overall, but three-quarters of fibroblastic sarcoids did.
• Regrowth is often fast. Removed sarcoids that return often do so within about six months, sometimes more aggressively than before.

Some quiet sarcoids do shrink on their own. A Swiss study found that nearly half of untreated sarcoids in young horses disappeared within five years, which is one reason your vet may suggest watching a small, stable lesion.

Why you shouldn't pick, band or paste a lump

It's tempting to deal with a small lump yourself. Please don't. Partial damage is the classic way a sleepy sarcoid turns angry.

• Picking or scratching off a crust injures the skin around it.
• Banding (tying off a lump with a rubber band) is something vets sometimes do for specific stalked sarcoids. At home, without knowing the type, it can leave tumor behind and stir up regrowth.
• Home and 'natural' pastes sold online can burn healthy skin, and some product labels themselves warn about use near the eyes or on ear cartilage. Some are caustic products that vets use only on carefully chosen cases.
• Cutting it off in the barn is never safe, for you or the horse.

Untreated sarcoids that get worse can ulcerate, bleed and attract flies. If your horse already has one, gentle fly control around it is fine; anything that touches the tumor itself is a vet decision. Our first aid kit checklist covers what's sensible to keep on hand.

Are sarcoids contagious?

Not in the simple way a cold is. The virus behind sarcoids comes from cattle, and researchers think it enters through broken skin.

• The virus has been detected on several common fly species, so flies are a suspected route.
• Contaminated tack, grooming kit or surfaces may play a role, though that's unproven.
• There's no firm scientific proof that sarcoids pass directly from one horse to another, but experts disagree, and some see clusters in herds and bonded pairs.

Practical takeaway: keep wounds clean, use good fly control, and give a horse with an open sarcoid its own brushes and tack. See our grooming basics for keeping kits clean.

When to call the vet and what they may discuss

Call your vet for any new lump, crusty patch or hairless spot that doesn't heal within a couple of weeks. Call sooner if a lump is:

• Growing quickly or changing shape
• Bleeding, raw or attracting flies
• Near an eye, on an eyelid or on the sheath or udder
• Under the saddle, girth or bridle
• One of several new lumps

Before the visit, take clear photos with a coin or ruler for scale, note when you first saw it and write down any changes. Photos every few weeks give your vet a real timeline.

Equine sarcoid treatment: what your vet may discuss

There's no single cure, and more than 40 therapies are in use. Depending on type, size and location, your vet may discuss:

• Careful monitoring for small, stable lesions
• Surgical or laser removal with a margin of healthy skin
• Freezing (cryotherapy)
• Creams or injections that stimulate the immune system or attack tumor cells, used under veterinary direction
• Radiation implants at specialty hospitals for tricky spots like eyelids
• Referral to a university hospital or a clinical trial

Many of these take several rounds, so ask about timelines, recheck visits and wound care up front. Learn more general health signs at Health Basics.

Buying a horse with sarcoids

Sarcoids don't automatically rule a horse out, but they affect value, insurance and future vet bills. During a pre-purchase exam, ask the vet to check the whole body, including the sheath, udder, groin and ears.

• Ask the seller about any past lumps and treatments.
• Ask your insurer whether existing sarcoids would be excluded.
• Think about location: a small lump on the neck is very different from one on an eyelid or under the girth.

The histotripsy trial: who can enroll and what to watch next

The Virginia-Maryland College of Veterinary Medicine needs four more horses to finish this phase. According to the trial details published Oct 14:

• The sarcoid must be fibroblastic or nodular, not occult (flat).
• The horse must not have been treated in the past six months, or the sarcoid must have come back after treatment.
• The trial can cover the consult, surgical fees and up to $1,500 in hospital costs.
• Horses that don't qualify may fit an option where a vet removes the tumor and sends it to the lab for study.

How to ask: call Large Animal Services at the Veterinary Teaching Hospital in Blacksburg, Virginia, at 540-231-4621. Be ready to email one photo showing where the sarcoid is on the body and close-ups from two angles. Involve your own vet: Bogers has offered to meet referring vets and their horses on-site in exchange for access to tumor tissue for research.

What to watch next: whether treated sarcoids stay away over months, not days, and whether a portable device makes the method practical outside a university hospital. Until then, the best tool is still an early vet visit. Follow new health stories on our trends page.