Last Updated on February 25, 2022 by Allison Price
Sarcoidos are the most common form of skin cancer in horses. They affect around 2% of the world’s population. They don’t spread (spread to distant places), but they can cause welfare problems, particularly in the “fibroblastic” ulcerated form. These may result from discomfort caused by the lesions or from fly interference. Also, administered treatments can cause discomfort. They can cause secondary ulceration and eyelid dysfunction in the most severe cases (Figure 1).
They are clearly not considered benign, and should be treated accordingly. Sarcoids can also have financial consequences due to their (sometimes very high) treatment cost and reduced resale values.
There is strong evidence that sarcoids can be caused by bovine papillomavirus. This virus is transmitted to flies by infected cattle and horses. It is not clear how the virus causes neoplastic (cancerous), change or whether it can cause disease in more than just one species. A (human) papillomavirus is also responsible for the majority of cervical cancer cases and an increasing number of head and neck tumors in humans. There is still much to learn about the consequences of infection with papillomaviruses across all species.
It is clear that the disease has a heritable component. Warmbloods have shown that there is a heritable component to the disease. Breeding two horses with sarcoid symptoms greatly increases the chance of them becoming sarcoids. There are also breed-related differences in sarcoid risks: Thoroughbreds have a higher risk of developing sarcoids, while Standardbreds are less likely. Lipizzaners appear to be more resistant.
Contrary to melanomas there is no predisposition for color and the risk of getting the disease doesn’t depend on gender. Certain gene variants, which have been identified in horses with sarcoids are also linked to virally-induced cancers in people. Although the reasons are not clear, it is possible that this association may be due to differences in immune function. This could explain apparent breed-specific variations in sarcoid risks.
There are many treatment options available for sarcoids. Not all cases will be treated the same way. Although sarcoids are often treated with no treatment at all, they can quickly become more severe and difficult to treat. It is important to seek immediate medical attention to prevent long-term complications. The treatment options include intra- or topical (injected into the lesion) chemotherapy, immune modulators, surgery, and radiotherapy. Although electrochemotherapy may seem to be a new treatment option, it requires multiple general anesthetics.
Figure 2 shows that the type and location of the lesion will play a major role in the selection of treatment. The majority of lesions located outside of the eye are treated with laser surgical excision. Periocular lesions can be treated using radiotherapy. This is the preferred treatment. The success rate for radiotherapy is around 90% and laser surgical excision is 83%. They are the most effective treatment option and pose the lowest risk to horses. These treatments are not suitable for every horse or lesion. The key is to choose the most successful method.
Recurrent sarcoids are more difficult to manage and can lead to a worse prognosis that those who were properly treated.
I’m Allison, born and raised in San Diego California, the earliest memory I have with horses was at my grandfather’s farm. I used to sit at the stable as a kid and hang out with my Papa while he was training the horses. When I was invited to watch a horse riding competition, I got so fascinated with riding!