Veterinary advice should be sought before applying any treatment or vaccine.


Sarcoids are a common, fibrosarcoma-like skin tumor affecting horses worldwide, with a 1-2% prevalence rate. Most are benign and not problematic, however they get to be a problem when they grow larger, ulcerate and located in areas that interfere with placement of tack and equipment on horses for athletic performance purposes. In one form of the disease, tumor cells can spread to the lymph nodes.

The exact pathogenesis of sarcoids in horses is not completely understood, however it has been strongly linked with bovine papilloma virus (BPV) type 1 or 2, due to the presence of BPV viral DNA isolated from 73-100% of equine samples studied. The transmission of BPV to horses is not well understood, however it has been demonstrated that it can be spread from horses to horses through direct contact with the skin of affected horses. Face flies are also implicated as possible vectors for transmitting the virus, as BPV DNA has been found in face flies removed from horses with sarcoid lesions.

Sarcoids can occur on any part of the horse's body, either singly or in clusters, however it is most frequently found on the ears, head and limbs. Sites of previous injuries to the horse's skin have an increased risk of developing sarcoids in the future. Thoroughbreds, Quarter Horses, Appaloosas, and Arabians have a genetic predisposition to developing sarcoids. Sarcoids are more frequently seen in young to middle-aged horses. Studies show that over 70 percent of sarcoids develop in horses less than 4 years of age.

There are six distinct forms of sarcoids in horses, classified according to gross appearance and behavior.
  • Occult: Flat and alopecic with mild cutaneous scaling. They are the most benign type of sarcoid which often remain quiescent with little change in appearance or growth.
  • Verrucous: Wart-like appearance with a raised, scaly, lichenified appearance with hair loss and epidermal thickening. This type is also generally benign.
  • Nodular: Firm, well-defined, subcutaneous lesions which are freely moveable and with normal or ulcerated skin.
  • Fibroblastic: Proliferative fleshy and ulcerated masses with local infiltration. They look similar to exuberant granulation tissue.
  • Mixed: May include any, or all, of the above-mentioned types and which tend to become progressively more aggressive as fibroblastic transformation occurs.
  • Malevolent: The most rare type of sarcoid and are aggressive, rapidly growing tumors that infiltrate locally along fascial planes and vessels. They are associated with a high recurrence rate and are the most aggressive form of sarcoid.
There are numerous treatment options available for horses with sarcoids. The cost of treatment varies widely and usually correlates with the number of treatment sessions required. The success rate of the various treatments varies depending on the number of sarcoids present, form(s), location(s), and stage of progression of the tumor(s).


Single or multiple lesions
Scaly, wart-like papules and plaques
Hypo or hyper-pigmentation, scaling or hair loss


  • History
  • Clinical signs
  • Physical exam
  • Biopsy
  • Virus isolation



RadiotherapyUses ionising radiation to kill neoplastic cells by damaging DNA and protein.
CryosurgeryInvolves the application of liquid nitrogen at -196 degrees Celsius either by spray or probe, to destroy tumor cells through the formation of intracellular ice and subsequent rupture of cell membranesC Rothacker et al., 2015
Bioabsorbable cisplatin beads91% (20/22) of horses with a 2-year follow up after treatment had complete resolution of the tumor.C Hewes 2007
Electrochemotherapy (ECT)A anticancer therapy that uses electrical field pulses to induce increased cell membrane permeability to antitumour hydrophilic drugs, such as cisplatin. Studies show ECT therapy was 99.5% (193/194) effective for sarcoid removal, for at least 4 years. However the size of the sarcoid significantly influenced the number of treatments required for its complete removal.Y Tamzali et al., 2012;C Rothacker et al., 2015
Interstitial brachytherapyAlso known as internal radiation therapy. It works through the use of a radiation source that is sealed in an implant and placed in or near the sarcoid.C Rothacker et al., 2015
Topical herbal preparationsC Rothacker et al., 2015
Topical ointmentsDaily topical application of 5% aciclovir cream for 2-6 months caused complete tumor remission for 68% (32/47) of horses with mild-type sarcoids; with no recurrences reported.
S Stadler et al., 2011; C Rothacker et al., 2015
Surgical removalUsing a laser, 83% (82/92) of horses showed no recurrence of the sarcoid removed. Horses with verrucose sarcoids were the form at an increased risk of recurrence.PC Compston et al., 2015; C Rothacker et al., 2015
ImmunotherapyRelies on local immune stimulation with the use of Chimeric virus-like particles (CVLPs) of BPV 1 L1-E7 or Bacillus Calmette-Guerin (BCG) cell wall extract as an intralesional injection to induce an immunological responseC Rothacker et al., 2015; S Mattil-Fritz et al., 2008
Autologous VaccineMultiple types are available. One type developed in Canada is based on the polymerization of antigenic tumor markers. 90% (19/21) horses that had this procedure had complete remission of the sarcoid. A second autologous vaccine developed by Epsy in 2008 can be performed in the field using sarcoid tissue frozen in liquid nitrogen and implanted back into the horse in subcutaneous pockets in the neck. This second vaccine showed an 80% (12/15) success rate for complete tumor regressionC Rothacker et al., 2015


Scientific Research

General Overviews

Clinical Trials

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Risk Factors

  • Previous skin trauma or open wounds

Commonly Affected Breeds

Quarter Horse iconAppaloosa icon