Sarcoids are the most common skin tumour encountered in horses. They are locally invasive, but not metastatic. This means they do not spread to distant sites within the body, but can grow and invade deeper into surrounding tissues.
There are six different types of sarcoid, recognized by their appearance, which can vary from a small, scaly, hairless area to large, ulcerated, rapidly growing lesions. Almost all involve the epidermis (the most superficial skin layer), with varying degrees of invasiveness. An individual sarcoid may contain a mixture of one or more forms. Sarcoids can also change from one form to another and progression is often unpredictable and sudden.
Sarcoids can be found on any part of the body but are most common around the eyes, mouth, sparsely haired areas (armpits and inner thigh), on the lower limbs, and at old wound sites. Thin-skinned horses are reportedly more susceptible to sarcoids and interestingly Lipizzaners appear resistant.
How or why some horses get sarcoids is not fully understood, but the bovine papilloma virus which causes warts in cattle has been implicated. It is thought that flies may spread the virus, and are attracted to secretions from the eyes, nose, wounds etc. This could explain why sarcoids are more common at these sites.
Treatment is often dictated by the particular sarcoid, and they frequently recur despite aggressive interveetion. The first attempt carries the best chance of cure, with a 30-40% decrease in prognosis with every subsequent attempt.
Treatment options include:
- Nothing - if not growing or interfering
- Surgical excision (sole treatment gives 35-50% recurrence rate)
- Injection of chemotherapy drugs - cisplatin, 5-fluorouracil - or bovine TB vaccine
- Cryosurgery - freezing with liquid nitrogen
- Creams applied directly to the lesion - toxic to cells (5-fluorouracil)
- Radiation (not in New Zealand)
A combination is often used. Occasionally sarcoids can spontaneously disappear.
If you are concerned that your horse may have a skin tumour, please contact us. Early intervention gives us the best chance of a successful outcome.