Equis ISSN 2398-2977

Eye: neoplasia - sarcoid

Contributor(s): Prof Derek Knottenbelt, Paul E Miller, Graham Munroe, Anna Hollis


  • Locally aggressive, fibroblastic tumor with high recurrence rate.
  • Most common type of skin tumor in horses.
  • Site: eyelids very common site but other body/head lesions can be evident.
  • Cause: strongly associated with infection with Bovine Papillomavirus types 1 and 2
  • Incidence: most common ocular tumor; 6 different types exist:, but occult, fibroblastic, nodular or mixed are most commonly seen affecting the eyelid.
  • Diagnosis: based on clinical signs. Can be confirmed by biopsy, but the latter may excacerbate the condition.
  • Treatment: depends upon many variables; radiation is considered to be the gold standard for any peri-ocular lesion but is expensive and has limited availability; BCG intra-lesional injections are very effective. for nodular lesions.
  • Prognosis: guarded; quite good with aggressive treatment in solitary lesions, but recurrence is likely and horses will remain liable to developing more sarcoids throughout their lifetime.



  • Epidemiology and behavior of sarcoids suggest involvement of an infectious agent.
  • Bovine papillomavirus types 1 and 2 strongly implicated in the development of equine sarcoids.
  • DNA of bovine papillomavirus types 1 and 2 have also been found in other types of spindle cell tumor in horses, and in normal skin.
  • Lesions resembling sarcoid have been produced experimentally by scarification of equine skin with homogenates containing bovine papillomavirus. (However, these lesions tended to resolve spontaneously with a host mounted immune response - neither of which appears to occur in natural sarcoid).
  • There is much work to be done to fully understand the pathogenesis of the equine sarcoid; similar to human papillomavirus and the link with various human cancers, it is likely to be an interaction with the virus, the host immune response, and genetic factors.

Predisposing factors


  • It has been suggested that the sarcoid lesions tend to occur on areas of skin prone to traumatic insult.


  • Locally invasive, non-metastatic, fibroblastic tumors of the skin which assume a variety of gross forms.
  • Capacity for infiltrative expansion in the dermis and subcutis.
  • Metastatic spread does not occur, but there are some reports of multiple small lesions occurring after incomplete surgical removal of one sarcoid or after autogenous vaccine usage.
  • Malevolent form shares some characteristics with aggressive, locally invasive neoplasms.
  • Fibroblastic types have long sinuous pegs of tumor tissue extending beneath the intact epidermis.
  • High tendency for sarcoids to recur.


  • Lesions tend to persist; some remain static, some worsen over time.
  • Spontaneous resolution is very rare.


  • Flies are likely to be involved in the transmission of Bovine Papillomavirus which is strongly implicated in the disease pathogenesis.


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Henson F M D & Dobson J M (2004) Use of radiation therapy in the treatment of equine neoplasia. Equine Vet Educ 16 (6), 315-318 Wiley.
  • Knottenbelt D C & Kelly D F (2000) The diagnosis and treatment of periorbital sarcoid in the horse - 445 cases from 1974-1999. Vet Ophthal 3, 2-23 PubMed.
  • Newton S A (2000) Periocular sarcoids in the horse - three cases of successful treatment. Equine Vet Educ 12 (3), 137-143 Wiley.
  • Knottenbelt D C & Walker J A (1994) Topical treatment of the equine sarcoid. Equine Vet Educ 6 (2), 72-75 Wiley.
  • Torrontegui B O & Reid S W J (1994) Clinical and pathologic epidemiology of the equine sarcoid in a referral population. Equine Vet Educ 6 (2), 85-88 Wiley Online Library.
  • Mohammed H O (1992) Factors associated with the risk of developing sarcoid tumours in horses. Equine Vet J 24 (3), 165-168 PubMed.
  • Pascoe R R (1991) Equine nodular and erosive skin conditions - the common and the not so common. Equine Vet Educ 3 (3), 153-159 Wiley.
  • Gorman N T (1985) Equine sarcoid - time for optimism. Equine Vet J 17 (6), 412-414 PubMed.
  • Lavach J D et al (1985) BCG treatment of periocular sarcoid. Equine Vet J 17 (6), 445-448 PubMed.
  • Trenfield K (1985) Sequences of papillomavirus DNA in equine sarcoids. Equine Vet J 17 (6), 449-452 PubMed.

Other sources of information

  • Knottenbelt D, Patterson-Kane J C & Snalune K L (2015) Clinical Equine Oncology. Elsevier Press.
  • Knottenbelt D, Edwards S & Daniel E (1995) Diagnosis and Treatment of the Equine Sarcoid. In: Practice. pp 123-129 (an excellent account of equine sarcoid, its diagnosis and treatment).