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A sarcoid is a benign tumour involving connective tissue that begins as a small wart-like growth but may progress, through stages of rapid growth to be about the size of a tennis ball. Generally sarcoids are dry scaly masses that are prone to bleeding. The main problems with sarcoids are secondary infection caused by physical interference, for example, the affected area rubbing on tack.

Sarcoids are believed to be caused by a virus; it has also been shown that Sarcoids are more common in older horses and on sites of previous trauma. Sarcoids are relatively common particularly in older horses, though severe cases amongst older horses are considerably less common.

Verrucous Sarcoids

Verrucous Sarcoids are typically dry lumps about the size of a golf ball, although the size may vary considerably.  They most often occur on head, chest, and shoulder and leg area. Normally lacking hair, they are not difficult to spot.

Fibroblastic Sarcoids

Fibroblastic Sarcoids are often a progression from the verrucous sarcoid which grows and splits or is otherwise physically damaged. This is the type that tends to cause more problems because it bleeds as it grows; some have been known to reach the size of a small football. Ulceration, fly-strike and secondary infection may all be complicating factors in this type of sarcoid. Growth rates do vary, these sarcoids sometimes lie dormant for several years. Occult Sarcoids are a flat form of sarcoid which again may become the fibroblastic type if damaged. 

Nodular sarcoid

·         Discreet solid nodules of variable size are common under the skin in the eyelid, armpit, inside thigh and groin regions.

·         They can be single or multiple (often they can be present in hundreds)

·         Many have no skin involvement (the skin can be moved freely over the surface) but some are firmly attached to the overlying skin (the skin cannot be moved over the surface of the nodule).

·         Some ulcerate and form bleeding masses.

Malevolent Sarcoid

·         This is the most aggressive type in which the tumours spread extensively through the skin with cords of tumour tissue interspersed with nodules and ulcerating fibroblastic lesions.

·         There are often some overlying verrucose and occult lesions.

·         It is a rare form but is most commonly encountered in the elbow and face areas.


Physical removal of the tumour through traditional surgery has been the normal practice. However there are multiple drawbacks to this technique including recurrence, accelerated growth, seeding  and scaring.

Cryosurgery is a technique whereby the area to undergo surgery is repeatedly fast-frozen to destroy all tissue before surgical removal. This decreases the likelihood of recurrence seeding. However the technique is not suitable for use near sensitive tissues such as the eyes.

Radiation therapy is a technique similar to that used to treat human cancer patients; the affected area is irradiated using a localised source. The drawbacks of this treatment are localized side effects of radiation and the need for specially trained staff and facilities.

Immunotherapy is a technique to activate the horse's own immune system against the tumour cells. Two different methods can be used:

·         Injection of BCG vaccine - Multiple injections into the tumour over a period of some weeks.

·         Introduction of Sarcoid tissue - Deactivated Sarcoid cells introduced under skin to build immune system response over several months.

These treatments are only suitable for small tumours and do take some time to work, however they do have the advantage of being relatively non invasive.


Sarcoids are not considered contagious, however they may be spread by contamination with living tumour cells. In other words any mechanism that might scrape cells off the tumour then place them back into another site, could lead to the formation of a new tumour. As previously mentioned, physical trauma to a sarcoid may accelerate the tumour activity.

Often small Sarcoids will remain relatively unobtrusive and cause few problems for a horse. On the other hand severe cases that resist treatment may require that the horse be destroyed on humane grounds. Research is continually improving the success rate of treatment; this combined with the fact that Sarcoids are benign tumours, means that in the majority of cases there is little risk to the horse's long term well being.