Equine sarcoids

Sarcoids are the most common equine skin tumors world-wide that has been heart-ache for horses and their owners for centuries. Although common, sarcoids vary greatly in their size and appearance, the nature in which they grow and potentially spread and the way they respond to treatment. It is this variability that makes sarcoids such a challenge for both owners and veterinarians.

Some Important Sarcoid Facts

· All equine species are susceptible – even donkeys and zebras.

· Although sarcoids are a type of cancer they do not spread to internal organs.

· Once a sarcoid horse, always a sarcoid horse! A horse with one sarcoid is likely to develop more.

· Sarcoids can develop anywhere on the horse’s skin, but more common sites include the chest, groin, sheath and face (especially around the eyes and mouth).

· Sarcoids are likely to recur, regardless of treatment.

· Trauma of any nature to a sarcoid is likely to aggravate it.

· No two sarcoids are the same; each sarcoid needs to be assessed on an individual basis.

· Sarcoids can be unpredictable in all aspects of their development and treatment.

· There is no ‘magic cure’ for sarcoids.

Types of Sarcoids

There are 5 broad classifications for equine sarcoids; occult, verrucous (warty), nodular, fibroblastic, and malevolent.

1. Occult sarcoids appear as roughly circular hairless areas of skin. They often are quite subtle early in their development and sometimes difficult to recognize. They can occasionally be mistaken for ‘ring-worm’ or even rub marks from tack.

2. Verrucous sarcoids are ‘wart-like’ in their appearance and are often grayish in color. The skin can crack easily and flakes of scale can often be rubbed off from the surface. They can appear singularly or in groups that merge into larger lesions.

3. Nodular sarcoids are firm, round, and can be singular or multiple and quite variable in size. Nodular sarcoids are usually covered by a layer of normal skin but can also be ulcerative. They are usually firmly attached to the skin overlying them but sometimes they are freely moveable under the surface.

4. Fibroblastic sarcoids are fleshy masses that grow quickly, bleed easily and often have ulcerated surfaces. They look very like exuberant granulation tissue (‘proud flesh’) and in fact, can develop at the site of a wound.

5. The malevolent sarcoid) is the most aggressive of all the sarcoid types. It can rapidly spread over a wide area of the horse’s body and grows in size just as quickly. The most likely appearance of the malevolent sarcoid is that of ulcerative nodular-like lesions group in large bundles. This condition can be so aggressive in nature that often there are no treatment options. Thankfully, malevolent sarcoids are very rare.

Sarcoid Treatment

Unfortunately there isn’t a magical cure-all treatment for sarcoids. There are over 50 different sarcoid treatments world-wide which clearly demonstrates that there is no one single method that will be effective in each and every case! Each and every sarcoid is different; they are unpredictable by nature and no matter how similar two sarcoids look, a treatment that works for one might not work for another. It is extremely important to remember that each sarcoid needs to be assessed by a veterinarian on an individual basis before any treatment is started. Inappropriate treatment can easily convert a simple sarcoid into something very nasty, very quickly.

Benign Neglect

Sometimes your veterinarian will advise you to just monitor a small sarcoid that has recently developed. They may suggest that you leave the sarcoid alone and watch for any signs of development or growth. Some sarcoids may stay very small without further development for years, so occasionally benign neglect is the treatment of choice. Of course, if the sarcoid starts to grow your veterinarian is likely to recommend an alternative treatment strategy.

Surgical Removal

Surgical removal of sarcoids is certainly a viable treatment but must always be done with caution as failure to completely remove the sarcoid will predispose its recurrence, often more aggressively. Surgical removal can be effective for small sarcoids in safe areas but the failure rate is relatively high. The decision to remove a sarcoid surgically weighs on many factors including the type of sarcoid, its location, vital structures near by and how the sarcoid might be impacting on the horse’s life. Nodular sarcoids often respond favorably to surgical removal.

Cryosurgery

The use of liquid nitrogen to freeze a sarcoid can be used for selective cases. Cryosurgery involves rapidly freezing and then slowly thawing tissues in order to kill the rapidly dividing tumor cells whilst sparing the normal cells. It can be time consuming and is only effective on small superficial lesions such as occult sarcoids. It can also be used on sarcoid tissue left following de-bulking surgery of very large sarcoids. There is a high recurrence rate following cryosurgery so is rarely a preferred treatment choice.

Intra-lesional Cisplatin or 5-Fluorouracil

These are chemotherapy drugs that have shown good results when injected directly into sarcoids. The drug is mixed with oil to give it slow-release properties and injected 3-4 times at 2 week intervals. As cisplatin is a toxic drug, care must be taken when injecting into the sarcoid. Local swelling and inflamma

-tion often occurs such that sarcoids treated with cisplatin often look worse before they look better.

Imiquimod (Aldara)

Imiquimod (Aldara cream) is an immune response modifier with potent antiviral and antitumor activity that is used for treatment of skin cancer and genital warts in humans. It has recently been used for treating sarcoids as well as aural plaques in ears, and has shown good results although it is prolonged treatment compared to other treatments. A light layer of cream is applied over the sarcoid initially three times weekly. Some local swelling usually occurs and again, sarcoids look worse before they get better. It may take 2-4 months of treatment to see a decrease in tumor size and so this is not a quick option. Cosmetic results are usually good, but can get expensive.

BCG Injection

This method works reasonably well for nodular and fibroblastic lesions around the eyes but is much less effective elsewhere and should not be used for sarcoids on the limbs as these often become much worse for some unknown reason! Injection of BCG (used for human TB vaccination) is performed 3 times at weekly intervals. The method has significant risks and careful supportive medication is required at the time of each injection. The risks relate to the chance that the horse will react adversely to the protein in the injection.

Xterra herbal paste

Xxterra or Sarc-Off (Indian Mud from North America)

containing zinc chloride and an extract of the root of the Sanguinaria canadensis plant has been used with some success, but will cause extensive tissue irritation.

Autogenous Sarcoid Implantation (Possibly Best Treatment Option)

Surgically remove several pencil-eraser-sized samples off the surface of tumor and freeze them by immersing them in liquid nitrogen to kill the virus. Once the sections have thawed, implant them along the crest of the neck. The crest is chosen because the skin is thin and the area relatively immobile so it heals quickly and, if there is a scar or white hair accumulation, the mane will cover it. So far, this technique has been more successful than conventional sarcoid treatments. The tumors typically regress between 90 and 120 days after treatment, but some have taken as long as 180 days to subside. None of the horses thus far has had a recurrence. The horses followed the longest are still sarcoid-free nine years later.

As you can see, sarcoid treatment is not easy! If you think your horse has a sarcoid, or would like to discuss possible treatment options of your horse’s sarcoids, please consult your veterinarian.

Dr. Darin Peterson, DVM, was born and raised on a horse and cattle ranch in Rosholt, S.D., and received his B.S. in Animal Science from SDSU. He concentrates most of his work time with large animals. He can be reached at 701-347-5496 or dpeterson@cassvetservice.com.