Bit & Bridle

Equine Sarcoids: Horse Skin Tumors

Other Names

  • Equine skin tumour
  • BPV-associated fibrosarcoma
  • Bovine papillomavirus-associated tumour

What are Equine Sarcoids?

Equine sarcoids are the most common skin tumours in horses, accounting for approximately 40% of all equine skin neoplasms. They are locally invasive fibroblastic skin tumours that do not metastasise (spread to internal organs), but their locally aggressive behaviour and tendency to recur after treatment make them clinically significant and often difficult to manage.

Sarcoids can occur on any part of the body but most frequently appear on the face (especially around the eyes and ears), groin, lower limbs, axilla (armpit region), and in wounds. They present in a variety of forms — from flat, barely visible lesions to large, ulcerating masses — and may remain stable for months before suddenly growing or multiplying. A horse may develop a single sarcoid or dozens simultaneously.

Any breed can be affected, but Thoroughbreds, Arabians, and their crosses appear at higher risk. Sarcoids are seen across all ages but are most commonly diagnosed in horses under 7 years. Once a horse has a sarcoid, it is at higher risk of developing more throughout its lifetime.

Causes

The development of equine sarcoids is strongly associated with infection by Bovine Papillomavirus (BPV), most commonly types 1 and 2. However, BPV alone does not explain the full picture — most horses exposed to BPV do not develop sarcoids, suggesting a significant genetic component to susceptibility.

  • BPV infection: The virus is present in the DNA of virtually all sarcoid tissues examined. Transmission from cattle or other horses may occur via biting flies, direct contact with infected tissue, or contaminated equipment.
  • Genetic predisposition: Certain MHC (major histocompatibility complex) haplotypes are associated with susceptibility — first-degree relatives of affected horses have a higher prevalence.
  • Wounds: Sarcoids frequently develop at sites of previous wounding or scarring, suggesting that trauma may initiate BPV integration in susceptible animals.
  • Flies: Biting flies (particularly Musca species) may mechanically transfer virus from infected tissue to wounds or mucous membranes on other horses.

Symptoms and Signs

Sarcoids are classified into six clinical types, each with distinct appearances:

  • Flat (occult) sarcoids: Subtle, circular, hairless, slightly thickened patches. Often the first sign. Commonly found on the face.
  • Verrucous (wart-like) sarcoids: Grey, dry, warty-textured lesions. More stable in behaviour.
  • Nodular sarcoids: Firm, spherical nodules beneath the skin, which may or may not be covered by normal skin. Common in the groin and axilla.
  • Fibroblastic sarcoids: Moist, ulcerated, proliferative masses. More aggressive and prone to rapid growth. Can be confused with proud flesh.
  • Mixed sarcoids: Combinations of the above types within a single lesion or on the same horse.
  • Malevolent sarcoids: The most aggressive form. Rapidly invasive lesions with multiple satellite nodules along lymphatic channels. Rare but extremely difficult to treat.

Diagnosis

Diagnosis is primarily clinical, based on the characteristic appearance and location of lesions:

  • Clinical examination: An experienced equine vet or dermatologist can often diagnose sarcoids confidently from their appearance alone
  • Biopsy: Histopathology confirms the diagnosis but is used with caution — incising or traumatising a sarcoid can cause it to grow more aggressively. Many specialists recommend treating rather than biopsying a suspected sarcoid.
  • PCR for BPV: Detection of BPV DNA in tissue can support diagnosis but is not routinely necessary
  • Differential diagnoses: Dermatophytosis (ringworm), warts (equine papillomatosis), fibroma, granulation tissue, and melanoma in grey horses

Treatment

No single treatment works reliably for all sarcoids, and recurrence rates are high regardless of method. Treatment choice depends on the type, size, location, and number of lesions:

  • Cisplatin chemotherapy: Intralesional or topical cisplatin in oil-based paste is effective for periocular and other accessible sarcoids. Multiple treatments required. Administered by a vet.
  • Liverpool cream (AW4-LUDES): A cytotoxic cream containing heavy metal compounds. Effective for many sarcoid types but can cause significant local reactions. Prescription only.
  • Electrochemotherapy (ECT): Combines chemotherapy with electrical pulses to enhance drug uptake. High success rates reported at specialist centres.
  • Cryotherapy: Freezing with liquid nitrogen. Most suitable for small, nodular lesions in accessible locations.
  • Surgical excision: Recurrence rates are high (up to 50-70%) if used alone. Best combined with adjunct therapy (cisplatin, ECT).
  • Laser surgery (CO2 laser): Precise removal with good haemostasis; useful for periocular lesions where surgical margin is limited.
  • Immunotherapy (BCG vaccine): Intralesional injection of Bacillus Calmette-Guérin (BCG) for periocular sarcoids. Can cause systemic reactions; used by specialists.
  • “Watch and wait”: For small, stable, flat sarcoids that are not growing or causing problems, careful monitoring without intervention is sometimes appropriate — particularly given that treatment can stimulate growth.

Prevention

There is no licensed vaccine against equine sarcoids. Practical prevention measures include:

  • Fly control: reduce biting fly populations with repellents, fly rugs, and stable management to minimise vector transmission
  • Wound management: prompt treatment of skin wounds reduces the risk of BPV integration at vulnerable sites
  • Avoid using shared equipment between horses that may have open lesions
  • Careful monitoring of horses known to be at higher genetic risk (horses with affected relatives)

Prognosis

The prognosis for equine sarcoids is variable and depends on the type and location. Small, occult or verrucous sarcoids in accessible locations have a reasonable treatment success rate. Large fibroblastic or malevolent sarcoids, particularly around the eye or in regions where adequate surgical margins cannot be achieved, are significantly more challenging and may recur repeatedly. Sarcoids that have been inappropriately traumatised or biopsied often become more aggressive. Referral to a specialist in equine dermatology or oncology is strongly recommended for complex or recurring cases. Useful guidance is available from the BEVA and the European College of Equine Internal Medicine.

When to Call the Vet

  • You notice a new skin lesion on your horse, particularly if hairless, warty, or growing
  • A known sarcoid is increasing in size, ulcerating, or changing in character
  • There are lesions near or around the eye — periocular sarcoids require specialist management
  • You are planning to purchase a horse with existing sarcoids — get an independent veterinary opinion on likely progression and treatment cost
  • Multiple new lesions are appearing rapidly — early specialist referral gives the best chance of effective management

Frequently Asked Questions

Can sarcoids be cured?

Not reliably. High recurrence rates are a hallmark of equine sarcoids regardless of treatment method. The goal of treatment is control — reducing the size, number, and growth rate of lesions. Some horses achieve long-term remission after treatment, but owners should be prepared for the possibility of recurrence, particularly with aggressive lesion types.

Are equine sarcoids contagious to other horses?

Not directly contagious in the way infectious diseases are. However, BPV can potentially be transferred via flies or shared equipment. Horses with active, ulcerating sarcoids should not share grooming tools or tack with other horses. The genetic component means that offspring of affected horses are at higher risk.

Should I buy a horse with sarcoids?

This is a judgement call that depends on the size, location, type, and number of lesions, and the intended use of the horse. Some horses have small, stable sarcoids that require minimal management. Others have aggressive, recurring lesions that are expensive and time-consuming to treat. Always have a pre-purchase examination by an independent veterinary surgeon who can assess the specific sarcoids present and advise on the likely management burden. Sarcoids that are not currently causing problems may deteriorate, particularly after stressful events or trauma to the area.

Why is biopsy risky with sarcoids?

Traumatising a sarcoid — whether through biopsy, incomplete surgical removal, or direct injury — can stimulate the lesion to grow more rapidly and aggressively. This is a well-recognised phenomenon in equine dermatology. When a sarcoid is suspected, most equine vets prefer to treat it empirically rather than incise it for biopsy. If histopathology is needed to confirm a diagnosis before committing to a treatment protocol, discuss the risks carefully with your vet beforehand.