What are sarcoids?

A sarcoid is a common type of skin tumour, affecting equids only (horses and donkeys). These comprise proliferation of a normal cell type, called fibroblasts, found in the skin and connective tissues in an abnormal way. Sarcoids can take several forms and can appear to be to be fairly benign (do not spread or grow), whereas some are more invasive, locally spreading and growing quickly. Fibroblast cells in other body tissues are not affected. Sarcoids do not spread to the internal organs.

Sarcoids are very widespread, persistent and although have low mortality can be a very significant nuisance and affect normal activities. They are still the subject of much frustration within the veterinary profession and we still have many unanswered questions about them.

Which horses get sarcoids?

Sarcoids can affect any horse, pony, donkey or mule (also zebras and przewalski horses! ). They can develop at any age and they occur everywhere around the world. There is no sex predilection (i.e no sex is predisposed to getting them), coat colour has no effect but some breeds do seem to be more susceptible, as do some families of horses, which shows there is a genetic susceptibility in some horses. There are many factors which influence the development of sarcoids, but we do not fully know what these all are.

What causes sarcoids?

There is debate over the cause although, there is some evidence that a viral antigen may be the underlying cause. It is thought that viral elements in cells change the behaviour of the fibroblasts at certain sites causing proliferation which can result in a visible tumour. Some horses are genetically more susceptible to getting sarcoids.

What do sarcoids look like?

Sarcoids vary in appearance greatly and they can appear similar to some other equine skin conditions. They occur anywhere on the body, but are more common at sites where skin and hair is thinnest such as eyelids, inner thighs, and sheath area. They are classified into 6 types based on appearance although all types are similar at a cellular level. The descriptors for these are - occult, verrucous, nodular, fibroblastic, mixed and malignant lesions but horses may have a selection of several lesions. Because they can be confused with other not so serious or other more serious conditions, it is always worthwhile getting them checked out by your vet.

Commonly, sarcoids can become ulcerated and bleed if rubbed or knocked and this can cause irritation, localise infection and pain (with or without swelling) and they are also a source of fly-worry. Sarcoid transformation at a wound site can occur and is a very serious cause for a wound to heal slowly. This occurs when a horse with sarcoids sustains a wound (trauma etc. ) and goes on to develop a sarcoid at the wound site. The appearance is very similar to exuberant granulation tissue (proud flesh). If any wound is failing to heal as expected, particularly on the limbs, sarcoid transformation should be considered your vet.

How do we diagnose sarcoids?

A vet should be consulted early if you suspect your horse has a sarcoid. Many are easily diagnosed tentatively based on a visual examination, whereas in others a small biopsy and histology may be required to diagnose, or to confirm a preliminary diagnosis.

How do we treat sarcoids?

There are many different treatment options available for sarcoids, but no single method is 100% effective. Sarcoids can be very difficult to treat, and costs of treatment can add up. Depending on the size, location and appearance of a sarcoid, several treatment options may be available, which may include only close monitoring but if treatment is advised, the sooner it is undertaken the better for a likely good outcome. Currently a multi-modal approach to treating them is considered to be the most effective for most horses. Radiotherapy is the most effective treatment but this is only available at one centre and is limited by lesion location and costs.

Your vet will discuss the treatment options most suited to your individual horse but at B&W these may include one of resection of ablation using a surgical laser, chemotherapy with citotoxic drugs (that can be enhanced by electrochemotherapy), application of a topical cytotoxic cream (aw4- ludes), ligation or a combination of treatments. There are also many anecdotal unproven treatments discussed in the lay-press. We do not recommend any homeopathic or herbal remedies or preparations as their safety and effectiveness is unproven early recognition and prompt treatment gives the best chance of long-term remission.

Can we prevent sarcoids?

Any wound on a horse which has a sarcoid at another site must be promptly dealt with, including veterinary input as soon as possible
it is still not clear as to how transmissible sarcoids are between horses, but it is common sense to exhibit caution, particularly during summer months, with regards to general fly control particularly when a horse has a wound and is co-grazing with another horse which has sarcoids. There is currently no vaccine to prevent sarcoids and it is unlikely that there will to be one in the near future, despite research efforts. Any horse which has sarcoids must be monitored regularly for signs of progression, as the rate is variable.

Should I buy a horse with sarcoids?

There are many considerations to buying a horse with sarcoids. Many small sarcoids do not interfere with the horses work but they all have the potential for progression. The location of the sarcoids is important as if they are in an area which is easily abraded/interfered with by tack then this can reduce the ability of the horse or pony to perform as required. However smaller, flatter sarcoids may not interfere with ridden work. A brood mare with sarcoids on her udder may resent a foal feeding from her udder. The other main consideration is expense and possible consequences on insurance for veterinary cover . Treatment of sarcoids can be costly (and is not always straight forward) and insurance companies will usually not insure the horse for treatment of these if he/she is purchased with sarcoids already present.