Equine Sarcoids are the most common skin tumours affecting the horse. They are a form of skin cancer and there is intense research into the cause (aetiology) and treatment of sarcoids. Sarcoids only affect horses and their kin including donkeys and mules. They can affect horses of any age but young horses appear predisposed.
Current opinion regarding the aetiology of sarcoids establishes a link between biting flies and sarcoids. Flies are thought to inject an oncogene into the skin and this oncogene stimulates the development of a cancerous mass i.e. a sarcoid. An oncogene consists of genetic material (for example DNA) that carries the ability to induce cancer. The oncogene that causes sarcoids is thought to have originated from a virus that stimulates the development of warts in cattle – the bovine papilloma virus.
Some sarcoids may remain dormant for the entire life of the horse therefore not requiring treatment; in rare cases a sarcoid will disappear entirely without treatment. However, sarcoids are very unpredictable in their nature and a small innocuous looking lesion sometimes rapidly develops into many large lesions in a short period of time.
Sarcoids can be grouped in to six different categories according to their appearance. The six different categories of sarcoid are listed below:
- Occult: flat hairless areas and there may be some subtle thickening of the skin.
- Verrucose: “warty” in appearance and can be very large in surface area.
- Nodular: masses that can vary in size from pea to melon!
- Fibroblastic: ulcerated and commonly bleed.
- Mixed: these lesions have characteristics of all or some of the above.
- Malignant: rare lesions that invade and spread aggressively.
There are several treatment options and no treatment provides a 100% chance of success. The most promising treatment for each lesion will depend upon any previous treatment, the category of sarcoid and its location.
Treatment options include: application (by a veterinary surgeon) of cytotoxic cream, ie “Liverpool cream” or AW4-LUDES, injection of other cytotoxic drugs such as Cisplatin, injection of Interferon, cryosurgery, surgical removal, injection of BCG (a vaccine usually used to immunise humans against TB) injection, and radiation therapy.
In most cases, if it is decided that the sarcoid requires treatment, photographs are taken and sent to Professor Knottenbelt MRCVS at Liverpool University. He will advise which treatment most likely to be effective and supply "Liverpool cream" at the best strength if appropriate.
Professor Knottenbelt has demonstrated that after each unsuccessful treatment tried on a sarcoid the chances of a complete cure are reduced by 25%. In other words you have approximately 5 attempts at treating a lesion before any further treatment will be useless. Treatment of a lesion includes all the above and alternative treatments such as homeopathy, “camrosa”, Tea tree oil etc. We strongly advise that no sarcoid is treated without first consulting one of the vets. It is very useful if a photograph (in good light and in focus!) can be taken and either sent or e-mailed to the office.