Sarcoids are a pain in the behind for horse owners. They are the most common of all the equine skin tumors, afflicting many horses. And because they vary widely in type and severity, there is no single treatment option that works best for all patients.
The good news is that, while these growths can be locally aggressive, they do NOT metastasize to other parts of the body, like malignant tumors do.
What causes equine sarcoids?
Researchers believe that two key factors contribute to sarcoid development in equines.
The first is viral. There is an association between sarcoid development and Bovine (cow) papillomaviruses, which are thought to be carried by flies. This is why, it is thought, sarcoids frequently occur in areas of recent wounds (which, of course, the fly population loves).
The second factor is genetics. Some horses carry a gene that seems to make them much more susceptible to sarcoids. This could explain why some horses develop sarcoids in multiple locations on their bodies, while other horses remain unaffected. Further supporting this theory, certain breeds are more likely to develop sarcoids (quarter horses), while the condition is rare in others (standardbreds).
What do they look like?
Sarcoids can affect the skin anywhere on the horse’s body, but the most common locations are the head and neck (especially around the eyes), lower limbs, and abdomen.
Appearance and behaviour
Sarcoids display a range of appearances and behaviours, including:
Verrucose: Wartlike, usually exhibits an irregular surface.
Fibroblastic: The growth is usually smooth and rounded. May bleed easily and could be mistaken for proud flesh.
Occult: Resembles thickened skin; often flat, hairless, and gray. Could be confused with trauma from rubbing.
Nodular: Usually round and covered by normal-looking, intact skin.
Mixed: Some sarcoids present like a mix of the types described above.
If you have a horse with a suspected sarcoid tumour, you may become overwhelmed by all the apparent treatment options, including old wives tales and advice received from fellow horse owners. Basically, though, the treatment options recommended by your veterinarian will comprise a few broad categories.
Occasionally, we’ll see a horse with a suspected sarcoid that has been present for a long period of time without any change. If the growth is located far away from the eyes and other sensitive structures and isn’t getting irritated by tack, the best approach may be to just leave it alone (but keep a close eye on it).
For smaller, discrete sarcoids, we often will surgically remove the growth as a first step (and then confirm that it is a sarcoid with histopathology). Unfortunately, regrowth of these tumors is extremely common, so follow-up treatment with other modalities is critical to reduce the risk of recurrence. Similarly, larger sarcoids may be surgically “debulked” prior to starting other forms of treatment.
Following surgery, cryotherapy (repeated, rapid freezing of the skin) is frequently used to help prevent recurrence.
Caustic creams may also be used as a follow-up to surgical removal. If the growth is small, we may try applying a caustic cream as a single modality to combat the tumour.
This treatment option is a more intense modality, often used for sarcoids around the eye. It involves injections of a preparation that “tricks” the immune system into seeing the sarcoid as “foreign.” This stimulates the immune system to attack and seek to destroy the affected tissue. There are also some topical immunotherapy creams available that have a similar method of action.
Chemotherapeutic agents can be injected, or surgically implanted, into sarcoid tumours. Similar to immunotherapy, there are chemotherapy creams available for use as topical treatments for certain cases.
As you can see, there are a variety of treatment options for sarcoids. Veterinarians determine the best treatment for each horse on a case-by-case basis. Typically, the location and size of the tumour are the main factors taken into account.