What Are Sarcoids?
Equine sarcoids are the most common skin tumour in the horse, accounting for 40% of all equine cancers. They are locally invasive tumours which are variable in appearance, location and rate of growth. Sarcoids are caused by Bovine Papilloma Virus, which may be spread by flies. Not all horses that are exposed to the virus develop sarcoids but, it appears that some horses are more susceptible than others. This also explains why horses that have sarcoids will stay susceptible and are more likely to grow additional sarcoids. People are often concerned about whether sarcoids are contagious because of the viral cause. No proof has yet been found that shows horse to horse contact can cause horses to develop sarcoids.
Sarcoids mainly occur around the head and in the groin and axilla area.
They seldom affect a horse’s usefulness, unless they are in a position likely to be abraded by tack. They do not usually resolve on their own and most horses develop multiple sarcoids.
Types of Sarcoids
Nodular sarcoids–are firm spherical nodules found under normal looking skin. They can be variable in size and can become ulcerated.
Verrucous sarcoids–are slow growing, flat scaly tumours that look like warts. They can also look like ringworm or scars.
Fibroblastic sarcoids–are fleshy lumps which often ulcerate, because they grow rapidly. They often occur in clusters and have an irregular shape.
Occult sarcoids–are flat hairless patches that occur mostly around the eyes, mouth and neck.
Malignant sarcoids –highly aggressive and these spread via lymphatic vessels, which results in lines of sarcoids spreading from the original sarcoid.
Sarcoids can, in some occasions, be confused with other tumours. Although a biopsy can give more information into what kind of tumour your horse has, taking a small sample of a sarcoid can cause the lump to start growing rapidly. Because sarcoids are the most likely diagnosis for these lumps, your vet will most likely suggest complete removal and possible sending the tissue off to a lab for histopathology, which can determine if the lump was in fact a sarcoid.
Treatment or removal of sarcoids are not always necessary but, when treatment is required it can prove difficult and possibly expensive. Sarcoids can regrow after treatment and no treatment as of yet is 100 % successful. Success rates vary between types of treatment. It is important to note that every treatment failure , reduces the success rates of future attempts.
- Ligation; where the sarcoid blood supply is cut off, causing it to shrink and drop off over time. Recurrence rates are more then 50%.
- Creams; there are various types, some more irritant to the skin than others and some have to be applied by your vet. They have a success rate of 40-60%.
- Injections; A chemotherapy drug injected into nodular and fibroblastic sarcoids causing the lesions to regress but can cause local swelling and sometimes injections need repeating.
- Radiation therapy; Iridium wires are inserted into a sarcoid to destroy it. It is the most effective treatment method but is very expensive and not widely available
- Laser Removal; is a surgical instrument that cuts into and vaporizes soft tissue with minimal bleeding. The wound that the horse is left with heals very well on its own. This treatment has one of the highest success rates with 80-90 % of horses not re-growing the sarcoid that was treated and, 70% of horses did not develop new sarcoids.
On the rare occasion that sarcoids regress on their own, these horses seem to develop immunity and do not develop further sarcoids. Please talk to your vet for more information on treatment options.