Equine Sarcoids: The Basics

Sarcoids are the most common skin tumour of horses worldwide, they have a wide range of appearances, behaviours, and characteristics which makes each sarcoid slightly different and make them challenging for vets to treat. They can develop anywhere on the body but are most commonly found in certain areas, including:

• The eyes/ears
• Muzzle/lips
• The chest and axilla (arm pit region)
• The sheath and in between the back legs

Sarcoids are believed to be caused by the bovine papilloma virus (BPV), but it appears that it requires genetically susceptible horses in order for sarcoids to develop as not every horse exposed to BPV will go on to develop sarcoids.  It is possible that they are spread contagiously but, as yet, the ability for sarcoids to be passed on by flies or direct horse-to-horse contact is unproven and there is no current evidence that horses affected by sarcoids are a threat to other horses developing them.

Types

Sarcoids are locally invasive tumours but don’t commonly metastasise (spread around the body) and are grouped into 6 broad categories:

• Occult: a flat patch of hair loss with a grey, scaly surface. These are often confused with ringworm as they have an annular (circular) lesion shape to them. Commonly seen on the face, neck and between the back legs
• Verrucose: wart-like, grey and scaly but goes deeper than the occult sarcoid and have a more irregular appearance
• Nodular: lumpy ‘grape like’ lesions. These can vary drastically in size and number, and are most commonly found around the groin and eyelids
• Fibroblastic: These can be quite aggressive in nature and can develop and alter rapidly. They are commonly fleshy masses that bleed easily and have ulcerated surfaces. They look like proud flesh and can often develop at the site of a wound.  These can be found anywhere on a horse body and can develop from the less aggressive types such as verrucose and nodular.
• Malevolent: this is the most aggressive type, it can spread and grow rapidly, and usually looks like a group of ulcerated, nodular type lesions. These are so aggressive that often there is no treatment options but thankfully they are rare.
• Mixed: this describes a sarcoid/group of sarcoids that show qualities of two or more of the classifications

They can appear as single lumps that can vary greatly in size (from a pin head to a small melon), or as clumps of more than one sarcoid.  The skin over sarcoids is often initially fine but can become ulcerated as the sarcoid continues to grow and develop, and can even become infected.  These can be especially frustrating to deal with during the summer due to flies and can up as non-healing sores.

Treatment

Sarcoids are a serious problem and even the appearance of one sarcoid should be taken seriously.  Where one sarcoid id present it is very common for more sarcoids to develop.  Early treatment is always more effective, and currently it would appear the treatment at under 4 years of age gives a slightly better prognosis.  Treatment will depend on the size, location, number and type of lesion present, and there is no one sure fire way to deal with all types of sarcoids. Sarcoids also have a high tendency for recurrence despite treatment. Treatment options include:

• Medical Treatments, including:
  • the immune stimulant Bacillus Calmette Guerin (BCG) vaccine (which is used to prevent Tuberculosis in people) being injected into the sarcoid itself
  • The injectable chemotherapy drugs cisplatin and Mitomycin C which act by interfering with DNA replication in the cells
  • Photodynamic treatment in which a chemical is applied to the surface of the tumour and then exposed to a specific type of light that activates the chemical and kills the cancer cells
  • The topical chemotherapy cream AW4-LUDES (‘Liverpool cream’)
  • Blood root cream
• Surgical treatments, including:
• Surgical excision
• Laser Surgery
• Cryosurgery
• Ligation and banding of nodular lesions

Surgical excision without additional therapy may not always yield the best results, these can be improved by following them up with cryosurgery or other treatment options but can often lead to a fairly high recurrence rate.

• Radiotherapy: local radiation has shown good results but is highly expensive. Iridium¹⁹² wires are used to deliver a radiation dose straight in to the tumour itself.  This means that it can be used in delicate areas (e.g. around the eyes) as it limits damage to neighbouring tissues. It can only be carried out at certain licenced premises.

Take Home Messages

1. Sarcoids are persistent and progressive skin tumours of all equid species (including donkeys and zebras) that are locally invasive but rarely metastatic
2. They are developed in response to exposure, in genetically susceptible horses, to BPV
3. They can occur anywhere but are commonly found on the head, chest, and groin
4. There are various types that each have their own characteristics and qualities and can require different approaches when considering treatment options
5. Horses that are found to have sarcoids at a pre-purchase exam (vetting) will have them excluded by insurers as a pre-existing condition and treatment can be costly