04/21/2024
What are sarcoids?
Sarcoids are the most common type of skin tumor seen in horses globally. They are most often seen in horses 1-7 years of age and are often found around the eyes, ears, neck, armpit, groin, and sheath.
Sarcoids are locally invasive and rarely regresses on their own. They do not spread to other tissues of the body but a horse with one sarcoid is likely to have more. While the tumor itself is not necessarily life-threatening, they are often found in inopportune areas such as where the girth sits. They may also become ulcerated, infected, and painful. Sarcoids are a detriment to the value, use, and welfare of the horse.
What causes sarcoids?
The exact details of how and why sarcoids form is an area of on-going research, but we know that multiple factors are involved. There appears to be a genetic predisposition. Appaloosa, Arabians, Quarter Horses, and Thoroughbreds are more likely to develop sarcoids than other breeds. Bovine papilloma virus has been consistently found within equine sarcoids. It is thought that this virus is transmitted by flies and contact with infected surfaces. Skin that is thin or inflamed is more likely to become infected by the virus and lead to sarcoid formation. The virus has been shown to induce tumor formation in the equine skin. Cattle infected with the virus build an appropriate immune response and clear the virus. Horses’ immune systems do not respond to the virus in the same way, allowing the virus to remain in the skin.
How are they diagnosed?
There are 5 broad classifications of sarcoids based on clinical appearance. They are occult, verrucous, nodular, fibroblastic, and malignant. Sarcoids can also be a combination of 2 or more of these categories. Sarcoids are often diagnosed based on clinical appearance but to know for sure, a biopsy is required. This involves taking a piece of the tumor and sending it to a histopathologist for microscopic evaluation. However, damaging the sarcoid in this way is likely to cause it to grow and transform. Alternatively, there is a lab test for the presence of bovine papilloma virus, which is highly suggestive of a sarcoid. A veterinarian will make recommendations for diagnosis and treatment based on size and location of the suspected sarcoid.
How are they treated?
Unfortunately, no one treatment has been found to be 100% effective at curing sarcoids. Sarcoids are very likely to recur after removal, and they often come back more difficult to treat. Some sarcoids may be left alone and monitored if they are in a location that is unlikely to be traumatized. A veterinarian may otherwise recommend treatment. Treatment options include surgical removal, cryotherapy (freezing), radiation therapy, chemotherapy, antiviral therapy, immune-modulating therapies, and/or a combination of these treatments.
Pictured here is an occult or "flat" sarcoid. For images of the other classifications visit https://equinesarcoid.co.uk/types (viewer discretion advised; some people may find the appearance of tumours to be graphic)
References:
Bergvall, K. E. (2013). Sarcoids. Veterinary Clinics of North America: Equine Practice, 29(3), 657–671. https://doi.org/10.1016/j.cveq.2013.09.002
Taylor, S., & Haldorson, G. (2012). A review of equine sarcoid. Equine Veterinary Education, 25(4), 210–216. https://doi.org/10.1111/j.2042-3292.2012.00411.x
Serving the North Okanagan
