Sarcoids are the most common form of skin tumour in the horse. They are often seen on the head, and they may be a problem if near the eye. They are also seen on the lower body, limbs and sites of previous injury. Trooper has a small sarcoid in between his front legs and has had it for a few years without having any problems from it.
Types of sarcoids
There are six types that occur.
- Occult has hair loss and they are often on the neck.
- Verrucous are wart like, cytokines transform the epidermis.
- A fibroblastic legion is the most ugly, they are red and weep. They are often seen on the pastern or the upper eyelid.
- The nodular form is where there is intact skin over them, the skin will move over them, this means they are easily removed with surgery. They are often seen around the eye or the inguinal region.
- They can be a mixed form.
- They can also be a malignant form, this is not common.
The treatment options currently available for sarcoids in the equine are limited. Surgical excision can be done. However, this may cuase recurrence and may enhance the growth. Some nodules may be OK to be removed in this way. Cyrosurgery may be done, this is when the tissue is frozen, mixed results have been seen using this method. This may cause scarring however and should not be done near the eye. Immunotherapy can be used such as using a vaccine, this would need to be given in a series of injections.This triggers an immune response and will help to heal it. However some horses are allergic to this. Radiotherapy can be used, this is more modern. Gold, radium and iridium are used and inserted into the legion. Topical chemotherapy may be used. There is a risk to the handler when using this as it is unstable. The smaller the sarcoid the easier to treat so it has to be done early. This method has been used for around 200 years.
The cause of sarcoids is not known. However, it is currently thought to be a bovine papilloma virus (BPV) related virus. It is also suspected that there is a genetic predisposition but then there has to be a trigger. Younger horses, ages 2- 6 show the highest prevalence. Most studies have not found a breed or sex linked predisposition. Though it has been linked with castration wounds in geldings. Mohammed et al (1994) found an increased prevalence in arabs and quarter horses compared to thoroughbreds. It is thought it could be carried by flies as it is more common around wound areas. This may explain the geographical variations that are seen with sarcoids.