Sarcoid Tumors: On Alert!

Last Updated on August 21, 2023 by Allison Price

These common skin cancers can be easily identified and treated.

The flat, hairless region of skin near the horse’s eyes was something I mentioned to my client the first time we met. She said it looked like a sarcoid tumour. It is important to act quickly, especially in this location. It would be a shame for it to spread to his eye.

[READ: Common Equine Skin Problems]

Photo credit: Jim Bortvedt. If you notice something similar on your horse’s skin it is time to contact your veterinarian. It is most likely a sarcoid tumour. If not treated promptly, it can become more severe.

She said, “Oh, no.” She said, “It’s been there all along, it’s just a small scar.” I was not convinced. She should keep an eye on the area and call me immediately if the hairless areas change in size or appearance. It was years later. Every time I saw him, I expressed my concern. I expressed my concerns at every visit. His owner assured me that there was nothing to be concerned.

The odd place grew until one day. It grew quickly. The once flat, hairless, small area was now a large, bulging mass that weighed in at a whopping golf ball size. What was once a small, hairless area of skin has become an aggressive sarcoid tumour.

We were able to save the eye with major surgery and several months of chemotherapy. However, it was not without considerable worry and expense. What is the lesson? Sarcoids can be sneaky. They are also very sneaky. They can disguise themselves as warts, scars, or little spots of fungus. They will remain on the horse’s skin for many years until they decide to grow fast.

Let me tell you some basic facts about Sarcoidos. It is worth your time to learn about sarcoids, which are the most common type in horses. You’ll learn what they are, how they develop, and how to treat them. You’ll also learn how to identify a sarcoid and why you should attack it before it’s too late.

Sarcoids 101
Since the early 1900s, horses have been able to recognize sarcoids. They are so common in horses that you will likely see them one day if they happen to be around. Over the years, we have learned that the bovine papillomavirus (BPV), is a possible cause. Research shows that 80 to 90% of all tumors are genetically susceptible to this common cattle virus. We don’t know how the virus is transmitted from horse to horse.

Sarcoids aren’t considered malignant, as they don’t spread to other parts of the body. Tumors that are more aggressive will grow quickly, causing havoc to local tissues. They can also be very difficult to eliminate, and often return after treatment, making them even more dangerous.

Sarcoid can occur in any part of your horse’s body. The most common locations are the chest, legs, genital area, and face. The most difficult and aggressive sarcoid to treat is one that appears on your horse’s forehead, particularly around his eyes.

Sarcoidos are so common, that any horse could be at risk. It is important to monitor your horse’s condition. Most tumors are more common in older horses, as “cells gone wrong” increases with age. However, sarcoids are more common in animals younger than 7. This suggests that there could be a genetic component. If your Quarter Horse horse is susceptible to developing sarcoid cancer, it may be a genetic factor. Because of the association with BPV, sarcoids may also be more common in horses with compromised immune systems. Sarcoids can also develop at the sites of scars and old wounds.

What is the greatest risk? Untreated sarcoid can grow more aggressively over time, making it more difficult to eradicate. The tumors will likely grow if treatment fails. It is important to be able to recognize a sarcoid as soon as it appears. This will allow you to get the treatment you need quickly and efficiently before it becomes too late.

[READ: Horse Lumps & Bumps]

It’s not a Wart…It is a Scar…It’s…
…A sarcoid! There were four types of sarcoid cancers that were previously known. They started with the benign and then progressed to the more aggressive. Mixed sarcoids can also be seen that have the same characteristics as the others. The term malevolent is also used to describe sarcoids which grow rapidly and cover large areas of the horse’s body. It is clear that early treatment and monitoring are crucial.

This guide shows you how to identify the four main sarcoid types.

Occult (flat).
It looks like: A flat, or slightly bumpy, patch of hairless skin. It may appear scaly at the surface.
Mistaken as: Hair loss caused by a tack or scar, fungus, allergic reaction, or ringworm.

Verrucous (warty)
This is A patch with hairless skin that has raised bumps and thick scales.
Mistaken for: Scar, fungus (ringworm), warts.

Credit: Four photos taken by Dr. Elizabeth Carr at Michigan State University

An easily moving mass beneath the skin. You may have normal skin on top, or an ulcerated surface.
Mistaken For: Cysts. Pressure/friction bumps (like those that form under the saddle, cinch), scar tissue from an injury or wound.

Looks similar to: Cauliflower-like mass with tissue, often with an ulcerative top.
Often mistaken for: Excessive Granulation tissue (proud meat); large, recurrent scars from injuries or wounds.

What should I do?
Call your vet if you suspect that your horse may have a sarcoid tumour. Your vet will need to perform a biopsy, which means he would take some tissue from the tumor and send it for analysis. A biopsy can prove to be difficult for a sarcoid because even a small amount can cause the tumor’s growth to be more severe.

A needle aspirate is possible in certain situations. Cells are taken from the tumor with a needle and an syringe and then examined under a microscope for sarcoid cells. Although this procedure is less likely than a biopsy to cause tumor inflammation, it can also be used to diagnose the condition. Recently, some tumor tissue samples were tested for BPV genetic material. This type of testing is notorious for false-negative results. The tissue test negative even if there is a sarcoid.

Your vet might make a presumptive diagnosis on the basis of the appearance of the cancer. This is to avoid the possibility of your pet becoming sarcoid angry from the biopsy.

Your vet might suggest that you start with a conservative approach (called “benign neglect”) if your horse’s tumor is small and not in a bad place. The vet will carefully measure the tumor and keep track of its appearance and size on a calendar. Treatment may not be necessary if the sarcoid remains the same. If the sarcoid shows any signs of change, particularly if it is getting larger, it may not be recommended to start treatment.

What is the best treatment for benign neglect? We wish we knew! There are many options available, as not everything works 100% of the time. Multiple treatments are required to conquer many tumors. These are some of the most popular treatments for sarcoid cancers.

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Surgical Removal: Your vet will remove the sarcoid from the skin and surrounding skin. They will also take care to not leave behind any tumor tissue. Laser surgery is possible if it is available. It can kill tumor cells and viral particles at the edges of the wound.

Advantages: Surgery is usually very economical and causes less scarring than other methods. It may be the only option when tumors are extremely large.

Cons: Tumors recurrence after surgery is quite common (as high at 80 percent has been reported). The theory is that viruses in the tissues can stimulate tumor growth, sometimes making it more aggressive than before. To minimize the chance of recurrence, other treatments such as chemotherapy may be necessary after surgery.

Cryosurgery is when liquid nitrogen is used to freeze tumors and kill them. Temperature probes can be used for larger tumors to ensure that the tumor’s center is sufficiently cold to be effective.

Credit: Jim Bortvedt. Liquid nitrogen can be used to freeze tissues in small tumors or more severe cases. Here I am freezing a Sarcoid using liquid nitrogen spray.

Advantages: Cryosurgery can be very cost-effective and efficient, particularly for small or superficial tumors. Sometimes, a tumor located far from the area being treated can spontaneously regress after treatment. This could be due to the horse’s immune system.

Cons Multiple treatments are often necessary. It can be difficult to identify redeveloping tumor tissue in scars.

[READ: Groom to Beat Equine Hair Problems]

Cisplatin, a chemotherapy drug known as cisplatin, is usually injected into the sarcoid in order to kill cancer cells. It can either be injected in a liquid form (mixed with oil so it will remain in the tissues for an extended period of time) or inserted through a very small incision in the form of a cisplatin-impregnated bead that dissolves slowly in the tissues. To reduce the possibility of a tumor regrowing, cisplatin is often used to treat the surrounding tissues.

The pros: When used effectively, tumors can often be completely resected without any residual scarring. Reports of success rates up to 90% are possible if the treatment is done correctly.

Cons It can also be toxic and difficult to manage.

Imiquimod: This cream modifies the immune response and has antiviral and anti-tumor properties.

The pros: This cream is easy to apply by the owner. It usually produces good cosmetic results. It can be purchased at most pharmacies.

Cons Tissue reaction can make the tumor look worse than it is improving. Larger tumors can be more expensive to treat.

Topical bloodroot (Xxterra strong> This cream treats and burns tumor cells as well as surrounding tissues. It can be used in a series of applications. After a treatment, the treated area will usually slough off within seven to ten days.

Advantages: This treatment is inexpensive and can usually be applied by the owner. With persistent treatment, success rates can be high.

Cons: A daily treatment of the horse for five days is recommended. It may also be necessary to repeat this treatment. The horse may experience swelling and pain after applying the cream. This can make it difficult for the horse to heal. The treated area may often become scarred.

The bottom line: Sarcoids can be very sneaky and are quite common. If you notice a strange hairless or bumpy area on your horse, be sure to call your veterinarian. These tumors are unlikely to cause any serious health problems, but they could be fatal. For success, it is important to start aggressive and effective treatment early.

Allison Price
Allison Price

I’m Allison, born and raised in San Diego California, the earliest memory I have with horses was at my grandfather’s farm. I used to sit at the stable as a kid and hang out with my Papa while he was training the horses. When I was invited to watch a horse riding competition, I got so fascinated with riding!