Sarcoid in Horses

Sarcoids are one of the most common tumors found in horses. It’s important to be able to identify different types of sarcoids in order to find the best treatment for your horse.

What Are Sarcoids in Horses?

Sarcoids are skin tumors that can develop anywhere on a horse’s body. They are relatively benign (harmless) masses under most circumstances unless they are irritated, in which case they can become more invasive and grow quickly.

Even if sarcoids grow quickly, there is no evidence at this time that they metastasize (spread) 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 appear to get them more frequently as well.

Types of Sarcoids in Horses

There are six types of sarcoids characterized by 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: A combination of any of the above characterizations

Signs of Sarcoids in Horses

Sarcoids are characterized by the formation of a mass or masses depending on the type of sarcoid mass that has formed. 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 together

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

Causes and Risk Factors of Sarcoids in Horses

There is some evidence that a bovine papillomavirus, which may be transmitted by flies, is involved in the formation of sarcoids. It’s always a good idea to equip your horse with fly deterrents such as fly spray during buggy seasons.

However, other factors are normally involved to predispose a horse to sarcoid formation such as wounds or genetics.

Diagnosing Sarcoids in Horses

Most sarcoids are diagnosed by their characteristic appearance. It’s under rare circumstances that 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 Sarcoids 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 continued monitoring at home without direct treatment unless the mass begins to grow aggressively or becomes irritating.

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 horse owners no longer want to leave them alone and will pursue treatment options.

There are a few options to try to decrease the size or remove a sarcoid that your veterinarian may discuss with you, 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 aggressive recurrence.

• Cryotherapy: This can be used in conjunction with surgical debulking (making the tumor smaller) and involves freezing the underlying tissue using liquid nitrogen. Cryotherapy can help to decrease 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.
  Keep in mind, this treatment can be very irritating and is not recommended for sarcoids on the ears because most horses will become resistant after several treatments.

• Xxterra: This herbal paste is another common topical treatment which irritates the tumor then causes it to slough off. The treatment can also be irritating to the skin and horses may become resistant to application after several rounds.

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

• BCG injections: Injections similar to vaccines that can be effective in a small subset of sarcoids but can also cause others to become worse and should be used with caution.

• Brachytherapy: This involves treating the sarcoid area with radiation. The treatment can be an expensive option that can be done at limited locations such as veterinary teaching hospitals.

Recovery and Management of Sarcoids 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 is often treated like an open wound.

Your veterinarian may prescribe topical treatments such as silver sulfadiazine, bandaging if needed, or topical/systemic antibiotics.

How To Prevent Sarcoids in Horses

While there are no guaranteed methods to prevent sarcoids from appearing on your horse, keeping horses clean and minimizing fly irritation may help minimize fly bites (which can transmit bovine papillomavirus).

Consider fly sprays, fly masks, or sheets if your horse is overly sensitive to fly bites.