Sarcoid in Horses

What is Sarcoid in Horses?

Sarcoids are one of the most common tumors found in horses. Sarcoids are skin tumors that can develop anywhere on the horse’s body. They are relatively benign masses under most circumstances unless they are irritated, in which case they can become more invasive and grow quickly (aggressive sarcoid). Even when they grow quickly, there is no evidence that they metastasize to other organs.

All age and breeds of horse can be affected by sarcoids, but geldings are considered more prone to them. Some breeds including Appaloosas, Quarter horses, and Arabians seem to get them more frequently as well. There are six types of sarcoids characterized on appearance:

• Occult: Flat and flaky plaques with hair loss.

• Verrucous: Wart-like masses.

• Nodular: Small, firm raised bumps under the skin.

• Fibroblastic: Fleshy masses that tend to ulcerate and bleed.

• Malevolent: Although all sarcoids can become aggressive and invasive when bothered or irritated, these masses are the most aggressive. They are easily irritated, grow quickly, and ulcerate frequently.

• Mixed: These masses are a combination of any of the above characterizations.

Symptoms of Sarcoid in Horses

Sarcoids are characterized by the formation of a mass or masses as described above. Additional symptoms depend on the location, and may include:

• Interference with tack: if located under the saddle, girth, bridles, or other harnesses.

• Ulceration and bleeding: if located where skin tends to rub.

• Lameness: if located at joints or the mass becomes large enough to limit or cause pain with motion.

Causes of Sarcoid in Horses

There is some evidence that a bovine papilloma virus, which may be transmitted by flies, is involved in the formation of sarcoids. However, other factors are normally involved to predispose a horse to sarcoid formation. Wounds and genetic predisposition may also increase the likelihood of sarcoids.

How Veterinarians Diagnose Sarcoid in Horses

Most sarcoids are diagnosed by their characteristic appearance. Rarely, a sample (fine needle aspirate or biopsy) can be taken to confirm that a mass is a sarcoid. Often, diagnostic sampling is avoided because it can risk aggravating the sarcoid and cause it to expand dramatically.

Treatment of Sarcoid in Horses

Most sarcoids, as long as they are small and not in an inconvenient location, can be treated through what veterinarians call “benign neglect.” This means doing nothing. If no trauma occurs to the site, sarcoids will usually stay the same shape and size and cause no issues for the horse.

When sarcoids are in inconvenient locations or have grown to sizes that begin to cause issues, most owners no longer want to leave them alone. There are a few options to try to decrease the size or remove a sarcoid, including:

• Surgical removal: Because these tumors can be so invasive, effective removal can be very challenging. If any tumor tissue is left behind, there is a large risk of very aggressive recurrence.

• Cryotherapy: This can be used in conjunction with surgical debulking and involves freezing the underlying tissue using liquid nitrogen. Cryotherapy can help decrease the chance of recurrence of sarcoids.

• Imiquimod (Aldara cream): Aldara cream is a very popular treatment. It is used in human medicine to treat skin cancers and genital warts. It works by causing the tumor tissue to die off. It can be very irritating and is not recommended for sarcoids on the ears because most horses will become non-compliant after several treatments.

• Cisplatin beads: Chemotherapeutic beads can be implanted directly into the mass and may successfully cause the mass to die off over time.

• BCG injections: Immunomodulatory injections (similar to a vaccine) have efficacy in a small subset of sarcoids but can also cause others to become worse and should be used with caution.

Recovery and Management of Sarcoid in Horses

Primary long term management of sarcoids involves preventing them from being traumatized to avoid aggravating them. If they become irritated and ulcerate, or removal is attempted, the site should be treated like an open wound. It should be kept clean and free of debris. Systemic antibiotics may be prescribed by a veterinarian as well.